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  • Geomagnetism, Rock Magnetism and Palaeomagnetism  (111)
  • Computational Methods  (36)
  • Other low-carbon energy technologies  (29)
  • 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring  (23)
  • Oxford University Press  (176)
  • American Geophysical Union  (20)
  • IEEE / Institute of Electrical and Electronics Engineers Incorporated  (1)
  • INGV  (1)
  • Molecular Diversity Preservation International  (1)
  • 2015-2019  (199)
  • 1990-1994
  • 1945-1949
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  • 1
    Publication Date: 2020-12-14
    Description: Explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks.
    Description: INGV-DPC “V2” and “Paroxysm”, FIRB-MIUR “Research and Development of New Technologies for Protection and Defense of Territory from Natural Risks”, and FP7-PEOPLE-IEF-2008 – 235328 Projects
    Description: Published
    Description: L02301
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: open
    Keywords: strombolian ; ejection velocity ; explosive eruption ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2020-12-15
    Description: This paper shows the main outcomes of the Puyehue volcano (Chile) eruption monitoring by means of multisensor remote sensing instruments working from thermal infrared (TIR) to microwave (MW) spectral range. Thanks to the use of Synthetic Aperture Radar (SAR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), the eruption evolution was observed, capturing the deformations of volcano edifice, the lava extension, as well as the information on ash and gas emitted. On the one hand, SAR Interferometry applied to ENVISAT-ASAR data allowed the estimation of the deformation occurred just before the beginning of the eruption and the subsequent deflation, with monthly sampling. On the other hand, with the combined use of the very high resolution (VHR) images taken by COSMO-SkyMed X-band SAR, and ENVISAT-ASAR ones, we were able to follow the lava deposition during the most intense phase of the eruption. Additionally, the joined exploitation of SAR and optical MODIS images allowed ash detection, also in cloudy sky conditions. Finally, the information gathered by both types of sensors allowed to highlight some volcanological features of the eruption and the relationship between surface deformation and the amount of ash and gases emitted by the volcano.
    Description: Published
    Description: 2786 - 2796
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: SAR interferometry ; Ash ; surface deformation ; lava field ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2021-02-10
    Description: Continuous gravity data collected near the summit eruptive vent at Kīlauea Volcano, Hawaiʻi, during 2011–2015 show a strong correlation with summit-area surface deformation and the level of the lava lake within the vent over periods of days to weeks, suggesting that changes in gravity reflect variations in volcanic activity. Joint analysis of gravity and lava level time series data indicates that over the entire time period studied, the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low—approximately 1000–1500 kg/m^3. The ratio of gravity change (adjusted for Earth tides and instrumental drift) to lava level change measured over 15 day windows rose gradually over the course of 2011–2015, probably reflecting either (1) a small increase in the density of lava within the eruptive vent or (2) an increase in the volume of lava within the vent due to gradual vent enlargement. Superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of Kīlauea’s summit and coincident changes in lava level. The unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation, perhaps indicating magma accumulation within, and withdrawal from, void space—a process that might not otherwise be apparent from lava level and deformation data alone. Continuous gravity data thus provide unique insights into magmatic processes, arguing for continued application of the method at other frequently active volcanoes.
    Description: Published
    Description: 5477–5492
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Kīlauea Volcano; gravity changes; lava lake; volcano monitoring ; 04. Solid Earth::04.02. Exploration geophysics::04.02.02. Gravity methods ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
    Publication Date: 2021-03-01
    Description: A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by comparable high values in September 2014, just before the onset of the new eruptive phase. The presence of a number of fresh and juvenile glassy shards in the erupted products increased between October 2014 and May 2015, suggesting the involvement of new magma with a composition similar to that erupted in 1864–1866. We conclude that the increase in 3He/4He at the summit fumaroles since October 2015 represents strong evidence of a new phase of magma replenishment, which implies that the level of activity remains high at the volcano.
    Description: Published
    Description: 3V. Proprietà dei magmi e dei prodotti vulcanici
    Description: 4V. Dinamica dei processi pre-eruttivi
    Description: 5V. Dinamica dei processi eruttivi e post-eruttivi
    Description: JCR Journal
    Keywords: Turrialba volcano ; eruptive activity ; 3He/4He ; fumarole gases ; glassy shards ; juvenile component ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.08. Volcanic arcs ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
    Publication Date: 2020-12-15
    Description: We have analyzed a focal mechanism data set for Mount Vesuvius, consisting of 197 focal mechanisms of events recorded from 1999 to 2012. Using different approaches and a comparison between observations and numerical models, we have determined the spatial variations in the stress field beneath the volcano. The main results highlight the presence of two seismogenic volumes characterized by markedly different stress patterns. The two volumes are separated by a layer where the seismic strain release shows a significant decrease. Previous studies postulated the existence, at about the same depth, of a ductile layer allowing the spreading of the Mount Vesuvius edifice. We interpreted the difference in the stress pattern within the two volumes as the effect of a mechanical decoupling caused by the aforementioned ductile layer. The stress pattern in the top volume is dominated by a reverse faulting style, which agrees with the hypothesis of a seismicity driven by the spreading process. This agrees also with the persistent character of the seismicity located within this volume. Conversely, the stress field determined for the deep volume is consistent with a background regional field locally perturbed by the effects of the topography and of heterogeneities in the volcanic structure. Since the seismicity of the deep volume shows an intermittent behavior and has shown to be linked to geochemical variations in the fumaroles of the volcano, we hypothesize that it results from the effect of fluid injection episodes, possibly of magmatic origin, perturbing the pore pressure within the hydrothermal system.
    Description: Published
    Description: 1181–1199
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: vesuvius ; stress inversion ; focal mechanisms ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
    Publication Date: 2021-04-07
    Description: Integrating geodetic, seismic, and petrological data for a recent eruptive episode at Mount Etna has enabled us to define the history of magma storage and transfer within the multilevel structure of the volcano, providing spatial and temporal constraints for magma movements before the eruption. Geodetic data related to the July–August 2014 activity provide evidence of a magma reservoir at ~4 km below sea level. This reservoir pressurized from late March 2014 and fed magmas that were then erupted from vents on the lower eastern flank of North-East Crater (NEC) and at New South-East Crater (NSEC) summit crater during the July eruptive activity. Magma drainage caused its depressurization since mid-July. Textural and microanalytical data obtained from plagioclase crystals indicate similar disequilibrium textures and compositions at the cores in lavas erupted at the base of NEC and NSEC, suggesting comparable deep histories of evolution and ascent. Conversely, the compositional differences observed at the crystal rims have been associated to distinct degassing styles during storage in a shallow magma reservoir. Seismic data have constrained depth for a shallow part of the plumbing system at 1–2 km above sea level. Timescales of magma storage and transfer have also been calculated through diffusion modeling of zoning in olivine crystals of the two systems. Our data reveal a common deep history of magmas from the two systems, which is consistent with a recharging phase by more mafic magma between late March and early June 2014. Later, the magma continued its crystallization under distinct chemical and physical conditions at shallower levels.
    Description: The petrological part of this study was supported by the FIR 2014 research grant to Marco Viccaro from the University of Catania (Italy), grant number 2F119B, title of the project “Dynamics of evolution, ascent and emplacement of basic magmas: case-studies from eruptive manifestations of Eastern Sicily”.
    Description: Published
    Description: 5659–5678
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Petrology ; eruption ; GPS ; volcano seismology ; Etna ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
    Publication Date: 2017-04-04
    Description: A new eruption started at Stromboli on August 6, 2014, which had been preceded by 2 months of increased Strombolian activity and several lava overflows from the craters. The eruption was characterized by a lava effusion in Sciara del Fuoco from a fracture at 650 m a.s.l. that lasted until November 13–17. Here we present the first geochemical observations of this eruption, based on the soil CO2 flux in the summit area, and on 3He/4He ratios in the thermal waters near Stromboli village. We infer that this eruption was triggered by the gradual replenishment of the feeding system by a CO2- and 3He-rich magma at the end of 2013 and after June 2014, suggested by the increase in 3He/4He ratio before eruption, which reached its highest value since 2007. We thus infer that this eruption was unusual and we finally speculate on the evolutionary scenario of post eruption.
    Description: Published
    Description: 2235–2243
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: Stromboli ; eruption ; soil CO2 flux ; 3He/4He ratio ; thermal waters ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
    Publication Date: 2017-04-04
    Description: The marine sector of the Campi Flegrei caldera has started to be monitored over the long-term with a seafloor equipment deployed in the Gulf of Pozzuoli from 2008. The equipment includes a set of geophysical, oceanographic and environmental sensors integrated in a marine platform that was specifically designed for real-time monitoring. This platform, named CUMAS (Cabled Underwater Multidisciplinary Acquisition System), was installed in the center of the Gulf at about 2.5 km south of Pozzuoli where the sea depth is about 100 m [Iannaccone et al., 2010]. The CUMAS system consists of a seafloor module connected by cable to a buoy (elastic beacon type) equipped with autonomous power supply systems, real-time data- transmission devices and a weather station. The core of CUMAS is the seafloor module that contains geophysical and oceanographic sensors, in particular, a three-component broadband seismometer, a best in class three axis MEMS accelerometer, a low-frequency hydrophone and a high-resolution sea bottom pressure recorder. A single-point acoustic, three-component, water-current meter and a water-temperature sensor were also installed to monitor some water local physical parameters. A set of status sensors, which also included a digital compass and a two-component digital tilt-meter, were added to track the attitude of the module over the course of the experiment. The marine monitoring system transmits the data in real-time and is integrated into the Monitoring Center in Naples managed by INGV-Osservatorio Vesuviano. A continuous GPS station has been installed since the end of 2011 on the top of the buoy. The elastic beacon buoy forms a structure which is rigidly connected by a mechanical cable to the ballast on the sea bottom, a submerged float at the base of the buoy maintains tension on the cable and ensure the overall buoyancy of the system. In this way, any vertical movement of the seafloor propagates rigidly to the emerged part of the buoy itself, allowing measurement of the vertical movement of the sea floor by the GPS station. The analysis of about 17 months of continuous GPS data, from January 2012 to May 2013, revealed an overall uplift of about 3-4 cm allowing a first measurement of vertical seafloor displacement in the Campi Flegrei caldera [De Martino et al., 2014]. A new opportunity to enhance the deployed system was given by a national project, EMSO-MedIT, which is providing the necessary resources to expand the data acquisition to other areas of the Gulf of Pozzuoli. New improved systems similar to CUMAS are going to be deployed in three additional marine sites of the Gulf of Pozzuoli and the existing tide gauges network will be renewed with state-of-art sensors. The overall new monitoring infrastructure will allow to extensively map the seafloor vertical displacement and to improve the interpretative models of the bradyseism phenomenon including a more accurate location of earthquakes in the marine areas and extending to lower magnitude values the detection of the seismic activity.
    Description: INGV, Comune di Nicolosi, Parco dell'Etna, Funivia dell'Etna
    Description: Published
    Description: Nicolosi (Catania) -I TALY
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: open
    Keywords: Monitoring System in Marine Sector ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 9
    Publication Date: 2020-02-24
    Description: This work arises from the field observations made during the civil protection emergency period connected to the 2007 Stromboli eruption. We observed changes in the shallow feeding system of the volcano to which we give a volcanological interpretation and the relative implications. Here we describe the processes that occurred in the upper feeding system from the end of the 2007 effusive eruption on 3 April to the renewal of the strombolian explosive activity at the summit craters (30 June), interpreted using multidisciplinary data. We used thermal camera data collected both from helicopter and from a fixed station at 400 m to retrieve the evolving summit crater activity. These data, compared with seismic signals and published geochemical records, allowed us to detail the shifting of the degassing activity within the crater terrace from NE to SW, occurred between 15 and 25 April 2007 prior to the resumption of the strombolian activity. In particular, from mid-April, a gradual SW displacement in the maximum apparent temperatures was recorded at the vents within the summit craters, together with a change in the very long period location and confirmed by variations in geochemical indicators (CO2∕SO2 plume ratios and CO2 fluxes) from literature. The shallow feeding system experienced a major readjustment after the end of the effusive activity, determining variations in the pressure leakage of the source, slowly deepening and shifting toward SW. All these data, together with the framework supplied by previous structural surveys, allowed us to propose that the compaction of debris accumulated in the uppermost conduit by inward crater collapses, occurred in early March, produced the observed anomalies. At Stromboli, major morphology changes, taking place in the following years, were anticipated by these small and apparently minor processes occurred in the upper feeding system. Other studies are relating similar changes to modifications of the eruptive activity also at other open-conduit volcanoes, so we believe that it may be important to have a constant monitoring of these phenomena in order to better understand their shallow feeding systems.
    Description: This paper was partially supported by a grant to S.C. (Project INGV-DPC Paroxysm V2/03, 2008–2010) funded by the Istituto Nazionale di Geofisica e Vulcanologia and by the Italian Civil Protection.
    Description: Published
    Description: 7376–7395
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Stromboli volcano ; thermal imaging ; multidisciplinary study ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
    Publication Date: 2017-04-04
    Description: An array of nine three-component broadband seismometers was deployed in two different configurations on Stromboli volcano. The analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano. These new observations are restricted to the low-frequency range below 1 Hz and underline, therefore, the superiority of broadband recordings over conventional short-period observations. Surprisingly simple wavelets indicate an initially contracting source mechanism. Gas-jets that could not be seen in a short-period seismic record at all, generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism. The analysis of particle motion and seismic array techniques permits a location of the seismic source. We find low-frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption-related events. A video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals.
    Description: Published
    Description: 749-752
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: N/A or not JCR
    Description: restricted
    Keywords: Stromboli ; volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 11
    Publication Date: 2017-04-04
    Description: High-speed imaging of explosive eruptions at Stromboli (Italy), Fuego (Guatemala), and Yasur (Vanuatu) volcanoes allowed visualization of pressure waves from seconds-long explosions. From the explosion jets, waves radiate with variable geometry, timing, and apparent direction and velocity. Both the explosion jets and their wave fields are replicated well by numerical simulations of supersonic jets impulsively released from a pressurized vessel. The scaled acoustic signal from one explosion at Stromboli displays a frequency pattern with an excellent match to those from the simulated jets. We conclude that both the observed waves and the audible sound from the explosions are jet noise, i.e., the typical acoustic field radiating from high-velocity jets. Volcanic jet noise was previously quantified only in the infrasonic emissions from large, sub-Plinian to Plinian eruptions. Our combined approach allows us to define the spatial and temporal evolution of audible jet noise from supersonic jets in small-scale volcanic eruptions.
    Description: INGV-DPC “V2” and “Paroxysm,” FIRB-MIUR “Research and Development of New Technologies for Protection and Defense of Territory from Natural Risks,” and FP7-PEOPLE-IEF-2008–235328 “NEMOH” ITN projects
    Description: Published
    Description: 3096–3102
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: jet noise ; volcano acoustics ; Stromboli ; Yasur ; Fuego ; strombolian eruption ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 12
    Publication Date: 2017-04-04
    Description: The fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide, due to the lack of suitable gas flux sensing techniques. In view of resumption of ground uplift (since 2005) and the associated variations in gas chemistry, Campi Flegrei, in southern Italy, is one of the restless calderas where gas flux observations are especially necessary. Here we report the first ever obtained estimate of the Campi Flegrei fumarolic gas output, based on a set of MultiGAS surveys (performed in 2012 and 2013) with an ad-hoc-designed measurement setup. We estimate that the current Campi Flegrei fumarolic sulphur (S) flux is low, on the order of 1.5–2.2 tons/day, suggesting substantial scrubbing of magmatic S by the hydrothermal system. However, the fumarolic carbon dioxide (CO2) output is ∼460±160 tons/day (mean±SD), which is surprisingly high for a dormant volcano in the hydrothermal stage of activity, and results in a combined (fumaroles + soil) CO2 output of ∼1560 tons/day. Assuming magma to be the predominant source, we propose that the current CO2 output can be supplied by either (i) a large (0.6–4.6 km3), deeply stored (〉7 km) magmatic source with low CO2 contents (0.05–0.1 wt%) or (ii) by a small to medium-sized (∼0.01–0.1 km3) but CO2-rich (2 wt%) magma, possibly stored at pressures of ∼100 to 120 MPa. Independent geophysical evidence (e.g., inferred from geodetic and gravity data) is needed to distinguish between these two possibilities.
    Description: Published
    Description: 4153–4169
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Campi Flegrei ; calderas ; gas output ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 13
    Publication Date: 2017-04-04
    Description: The interpretation of dynamic processes that occur in volcanic calderas is not simple. The ground deformations and the local seismicity, which in other volcanic contexts are usually regarded as precursors to eruption, in caldera environment in many cases are not followed by any eruption. We formulate a general hypothesis that can explain these behaviors. Our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas. In order to investigate the reliability of this hypothesis, we developed a dynamic model of sill intrusion in a shallow volcanic environment. In our model, the sill, fed by a deeper magma reservoir, intrudes below a horizontal elastic plate, representing the overlying rocks, and expands with axisymmetric geometry. The model is based on the numerical solution of the equation for the elastic plate, coupled with a Navier-Stokes equation for simulating the dynamics of the sill intrusion. We performed a number of simulations, with the objective of showing the main features of the model. In the experiments, when the feeding process stops, the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence. Under certain conditions the subsidence can occur even during the intrusion of the sill. The stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front. The features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature.
    Description: Published
    Description: 3986–4000
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: sill intrusion ; caldera ; volcano geodesy ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 14
    Publication Date: 2017-04-04
    Description: Mt Etna volcano (Italy) typically generates lava fountains and Strombolian eruptions from the summit craters, producing significant emissions of tephra which may cause moderate to high impact both in the atmosphere and on the ground. However, we have also witnessed a number of minor ash emissions that, although far less powerful, may pose considerable volcanic hazards. In this paper, we deal with three ash emissions occurring in 2010 (8 April at Southeast Crater, 25 August at Bocca Nuova, and 14–15 November at Northeast Crater), correlating their volcanological features with the associated seismoacoustic signals. We provide details regarding the chronology, eruption column, dispersal of the deposit, and texture (grain size, componentry and morphology) of the emitted ash. Each eruptive episode has also been characterized by means of seismo-acoustic analyses evaluating the volcanic acoustic-seismic ratio (VASR). Furthermore, the source of volcanic tremor recorded from March to December 2010 was localized. The joint volcanological and seismo-acoustic analyses allowed distinguishing two main kinds of ash emissions: types a (8 April and 25 August) and b (14–15 November). Regarding the former, the accumulation of gas below a dense cap rock obstructing the conduit vent, giving rise, with the uncorking, to impulsive explosivity, was hypothesized. The latter type instead is characterized by a longer-lasting and less explosivity, likely due to the existence of open conduit conditions. Therefore, type b ash emissions are less hazardous than type a. This simple model, regarding minor explosive activity, may constitute a starting point to assess the volcanic risk from unexpected explosions.
    Description: Published
    Description: 51-70
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: reserved
    Keywords: Mt Etna ; seismo-acoustic signals ; ash emissions ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 15
    Publication Date: 2017-04-04
    Description: Between January 2011 and April 2013, Mt. Etna's eruptive activity consisted of episodic intra-crater strombolian explosions and paroxysms from Bocca Nuova, Voragine, and the New South-East (NSEC) summit craters, respectively. Eruptions from NSEC consisted of initial increasing strombolian activity and lava flow output, passing to short-lasting lava fountaining. In this study we present seismic, infrasound, radiometric, plume SO2 and HCl fluxes and geodetic data collected by the INGV monitoring system between May 2012 and April 2013. The multi-parametric approach enabled characterization of NSEC eruptive activity at both daily and monthly time scales and tracking of magma movement within Mt. Etna's plumbing system. While seismic, infrasound and radiometric signals give insight on the energy and features of the 13 paroxysms fed by NSEC, SO2 and halogen fluxes shed light on the likely mechanisms triggering the eruptive phenomena. GPS data provided clear evidence of pressurization of Mt. Etna's plumbing system from May 2012 to middle February 2013 and depressurization during the February-April 2013 eruptive activity. Taking into account geochemical data, we propose that the paroxysms' sequence represented the climax of a waxing-waning phase of degassing that had started as early as December 2012, and eventually ended in April 2013. Integration of the multidisciplinary observations suggests that the February-April 2013 eruptive activity reflects a phase of release of a volatile-rich batch of magma that had been stored in the shallow volcano plumbing system at least four months before, and with the majority of gas released between February and March 2013. This article is protected by copyright. All rights reserved.
    Description: European FP7 MED-SUV (MEditerranean SUpersite Volcanoes). Grant Number: 308665 European Research Council European FP7 (FP/2007-2013)/ERC. Grant Number: 279802 SIGMA (Sistema Integrato di sensori in ambiente cloud per la Gestione Multirischio Avanzata)
    Description: Published
    Description: 1932–1949
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Mt. Etna ; paroxysmal activity ; SO2 and HCl fluxes ; infrasound and seismic signals ; radiometry ; ground deformation ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 16
    Publication Date: 2017-04-04
    Description: We present the results of laboratory experiments on the aggregation and disaggregation of colliding volcanic ash particles. Ash particles of different composition and size 〈90 µm were held in turbulent suspension and filmed in high speed while colliding, aggregating, and disaggregating, forming a growing layer of electrostatically bound particles along a vertical plate. At room conditions and regardless of composition, 60–80% of the colliding particles smaller than 32 µm remained aggregated. In contrast, aggregation of particles larger than 63 µm was negligible, and, when a layer formed, periods when disaggregation (mainly by collisions or drag) exceeded aggregation occurred twice as frequently than for smaller particles. An empirical relationship linking the aggregation index, i.e., the effective fraction of aggregated particles surviving disaggregation, to the mean particle collision kinetic energy is provided. Our results have potential implications on the dynamics of volcanic plumes and ash mobility in the environment.
    Description: INGV-DPC project V1 “Probabilistic evaluation of volcanic hazard”; EU Seventh Programme FP7 “MED-SUV” grant agreement 308665
    Description: Published
    Description: 1068–1075
    Description: 3V. Dinamiche e scenari eruttivi
    Description: 2IT. Laboratori sperimentali e analitici
    Description: JCR Journal
    Description: restricted
    Keywords: volcanic ash ; disaggregation ; experimental modeling ; volcanic plumes ; aggregation processes ; colliding particles ; sticking rate ; 01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 17
    Publication Date: 2017-04-04
    Description: Piton de la Fournaise (PdF) is recognised as one of the world’s most active volcanoes in terms of eruptive frequency and the substantial quantity of lava produced. Yet, with the sole exception of rather modest intracrateric fumarole activity, this seems to be in contrast with an apparent absence of any type of natural fluid emission during periods of quiescence. Measurement campaigns were undertaken during a long-lasting quiescent period (2012-2014) and just after a short lived summit eruption (June 2014) in order to identify potential degassing areas in relation to the main structural features of the volcano (ex. rift zones) with the aim of developing a broader understanding of the geometry of the plumbing and degassing system. In order to assess the possible existence of anomalous soil CO2 flux, 513 measurements were taken along transects roughly orthogonal to the known tectonic lineaments crossing PdF edifice. In addition, 53 samples of gas for C isotope analysis were taken at measurement points that showed a relatively high CO2 concentration in the soil. CO2 flux values range from 10 to 1300 g m-2 d-1 while 13C are between -26.6 to -8‰. The results of our investigation clearly indicate that there is a strong spatial correlation between the anomalous high values of diffusive soil emissions and the main rift zones cutting the PdF massif and, moreover, that generally high soil CO2 fluxes show a d13C signature clearly related to a magmatic origin.
    Description: INSU (CNRS) and La Réunion Préfecture (Projet pour la quantification de l’aléa volcanique à La Réunion)
    Description: Published
    Description: 4388–4404
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: CO2 soil degassing anomalies at Piton de la Fournaise ; d13C magmatic signature ; Close link between anomalous CO2 degassing and the main seismotectonic structures ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 18
    Publication Date: 2017-04-04
    Description: This paper focuses on the chemical composition changes in soil gases through both a theoretical model and laboratory experiments. The model describes the one-dimensional mass transfer process, which is triggered by changes in the flux parameters of the system, and the time-dependent evolution of the composition of the soil gases as a function of i) the pristine gas mixture, ii) the diffusivity of the chemicals, and iii) the thickness of the transited medium. Carbon dioxide (CO2), hydrogen (H2), and helium (He) were used in a laboratory-scale flux simulator to investigate the evolution of the gas composition profile in an artificial soil of constant thickness. The agreement between the theoretical calculations and the experimental results supports the validity of the model. Our results indicate a good reproducibility of the transient changes in the concentrations of CO2, He, and H2 in CO2-rich gas mixtures that contain He and H2 as trace gases. Finally, the theoretical results were used to analyze the H2 and CO2 continuous monitoring data collected at Etna volcano in 2010
    Description: Published
    Description: 1565–1583
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: JCR Journal
    Description: open
    Keywords: Soil gases ; Volcanic gas composition ; Hydrogen ; Carbon dioxide ; CO2 ; Helium ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 19
    Publication Date: 2017-04-04
    Description: On 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel-1A ascending interferogramswere calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upperpart of the volcano.Despite snowcover onthe summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtainingmore detail onthe grounddeformation pattern on the upper eastern side of the volcano. Three-dimensional GPS displacements inversion located a very shallow NE-SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field
    Description: Published
    Description: 2727–2733
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Sentinel-1A interferogram details the ground deformation field ; GPS data are analyzed for modeling the dyke intrusion ; Data comparison highlights an incipient slope failure ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 20
    Publication Date: 2017-04-04
    Description: During volcanic eruptions, measurements of the rate at which magma is erupted underpin hazard assessments. For eruptions dominated by the effusion of lava, estimates are often made using satellite data; here, in a case study at Mount Etna (Sicily), we make the first measurements based on terrestrial laser scanning (TLS), and we also include explosive products. During the study period (17–21 July 2012), regular Strombolian explosions were occurring within the Bocca Nuova crater, producing a ~50 m-high scoria cone and a small lava flow field. TLS surveys over multi-day intervals determined a mean cone growth rate (effusive and explosive products) of ~0.24 m3·s−1. Differences between 0.3-m resolution DEMs acquired at 10-minute intervals captured the evolution of a breakout lava flow lobe advancing at 0.01–0.03 m3·s−1. Partial occlusion within the crater prevented similar measurement of the main flow, but integrating TLS data with time-lapse imagery enabled lava viscosity (7.4 × 105 Pa·s) to be derived from surface velocities and, hence, a flux of 0.11 m3·s−1 to be calculated. Total dense rock equivalent magma discharge estimates are ~0.1–0.2 m3·s−1 over the measurement period and suggest that simultaneous estimates from satellite data are somewhat overestimated. Our results support the use of integrated TLS and time-lapse photography for ground-truthing space-based measurements and highlight the value of interactive image analysis when automated approaches, such as particle image velocimetry (PIV), fail.
    Description: Published
    Description: 14967 - 14987
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: open
    Keywords: lava flow; scoria cone; effusion rate; terrestrial laser scanning; time-lapse photography; Mt. Etna ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 21
    Publication Date: 2017-04-04
    Description: To evaluate the volcanic processes leading to the 25–26 October 2013 lava fountain at Mount Etna, we jointly investigated gravity, GPS, and DInSARmeasurements covering the late-June to early-November time interval. We used finite element modeling to infer a shallow magmatic reservoir which (i) inflated since July 2013, (ii) fed the volcanic activity at the summit craters during 25–26 October, and (iii) deflated due to magma drainage related to this volcanic activity. We suggested that this reservoir belongs to a shallow volume, which is located beneath the summit area and is replenished by magma rising from deep reservoirs and fed the short-term volcanic activity, representing a persistent shallow magmatic plumbing system of Etna. In addition, the model results show that there is a large discrepancy between the erupted and shallow reservoir deflation volumes, which could be reasonably attributable to a highly compressible volatile-rich magma.
    Description: Published
    Description: 3246–3253
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: open
    Keywords: Gravity and deformation signatures of the 26 October 2013 Mount Etna lava fountain ; Integrated finite element-based inversion of gravity and GPS data ; Inference on a highly compressible volatile-rich magma in the magmatic reservoir ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 22
    Publication Date: 2021-12-15
    Description: Relationships between frequency and intensity of volcanic eruptions are actively sought by geophysicists for both monitoring and research purposes. By analyzing surveillance videos of persistent volcanic activity at Stromboli (Italy), we derived the frequency and jet height of 〉4000 explosions that occurred in 72 h-long time windows sampled yearly from 2005 to 2009. We found a positive relationship linking explosion frequency and jet height (linked to eruption intensity) when averaging the two parameters over time intervals from hours to days, with a stronger correlation for longer intervals. We interpret this behavior as the response of the magmatic system to variable influx of magma and gas at depth, increased flux at depth causing more frequent and stronger explosions at the surface. This relationship entails concurrent control of source processes over explosion frequency and intensity, directly impacting modeling of explosion sources at persistently active volcanoes in general and hazard assessment at Stromboli in particular.
    Description: DPC-INGV Project V2 “Paroxysm”
    Description: Published
    Description: 1–5
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: reserved
    Keywords: Stromboli ; Strombolian frequency ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 23
    Publication Date: 2023-01-19
    Description: In situ measurements have been the basis for monitoring volcanic gas emissions for many years and—being complemented by remote sensing techniques—still play an important role to date. Concerning in situ techniques for sampling a dilute plume, an increase in accuracy and a reduction of detection limits are still necessary for most gases (e.g., CO2, SO2, HCl, HF, HBr, HI). In this work, the Raschig-Tube technique (RT) is modified and utilized for application on volcanic plumes. The theoretical and experimental absorption properties of the RT and the Drechsel bottle (DB) setups are characterized and both are applied simultaneously to the well-established Filter packs technique (FP) in the field (on Stromboli Island and Mount Etna). The comparison points out that FPs are the most practical to apply but the results are errorprone compared to RT and DB, whereas the RT results in up to 13 times higher analyte concentrations than the DB in the same sampling time. An optimization of the analytical procedure, including sample pretreatment and analysis by titration, Ion Chromatography, and Inductively Coupled Plasma Mass Spectrometry, led to a comprehensive data set covering a wide range of compounds. In particular, less abundant species were quantified more accurately and iodine was detected for the first time in Stromboli’s plume. Simultaneously applying Multiaxis Differential Optical Absorption Spectroscopy (MAX-DOAS) the chemical transformation of emitted bromide into bromine monoxide (BrO) from Stromboli and Etna was determined to 3–6% and 7%, respectively, within less than 5 min after the gas release from the active vents.
    Description: Published
    Description: 2797–2820
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: plume ; volcano ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 24
    Publication Date: 2015-08-16
    Description: Natural gas is an extremely important bridge fuel to a low-carbon energy economy for improving local air quality. Coal to synthetic natural gas (SNG) is an effective way to convert the high-carbon energy (coal) into the low-carbon energy with rich hydrogen (natural gas). For the modern coal to SNG industry, the high-temperature methanation (HTM) catalyst plays an important role, and the advanced evaluation process should necessitate the elimination of mass transfer effect. Some simple but effective model catalysts, such as slab and sphere, can be very helpful in defining the reaction conditions, and thus facilitating the evaluation process for real HTM catalysts. In this work, slab and sphere model catalysts were adopted to derive mass transfer and reaction-coupled equations, the numerical methods were used to solve the coupled equations for the concentration profiles in catalysts, and the effectiveness factors were accordingly calculated. By taking advantage of the Thiele module and the Weisz–Prater module , the criteria for the elimination of mass transfer effect in the HTM catalyst evaluation process were successfully defined. This work also complements the Weisz–Prater criterion by incorporating ‘negative reaction orders’.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 25
    Publication Date: 2015-08-16
    Description: The energy expended for conditioning buildings around the world is worryingly large and increasing every year. Currently, almost half of houses around the world use some type of energy-expensive conventional air-conditioning system. These systems are high emitters of gases such as carbon dioxide and so high contributors to climate change. Consequently, alternatives must be considered. Earth–air heat exchangers (EAHEs) and phase-change materials (PCMs) may be options; they have, however, limitations. This paper proposes a novel hybrid space-conditioning system combining EAHEs with PCMs, which uses surfaces as sources of heating or cooling to provide better temperature distribution across a space and comfort enhancement with low energy use. The idea is to use an EAHE to provide cool air to discharge the PCM, consequently helping to overcome most of the limitations of both strategies. Two of a series of experiments undertaken to test the proposed system are reported in this article. The EAHE + PCM system compared with a reference room could decrease temperature swings by up to 47%. The system was proved to work although further work is required to make it commercially viable.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 26
    Publication Date: 2015-08-16
    Description: Passive convective heat transfer enhancement can be achieved by improving the thermo-physical properties of the working fluid, changing flow geometry or both. This work presents a numerical study to investigate the combined effect of using helical coils and nanofluids on the heat transfer characteristics and pressure losses in turbulent flow regime. The developed computational fluid dynamics models were validated against published experimental data and empirical correlations. Results have shown that combining the effects of alumina (Al 2 O 3 ) nanoparticles and tube coiling could enhance the heat transfer coefficient by up to 60% compared with that of pure water in straight tube at the same Reynolds number. Also, results showed that the pressure drop in helical coils using Al 2 O 3 nanofluid for volume fraction of 3% was six times that of water in straight tubes (80% of the pressure drop increase is due to nanoparticles addition), while the effect of Reynolds number on the pressure drop penalty factor was found to be insignificant.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 27
    Publication Date: 2015-07-30
    Description: Seismic waves sensitive to the outermost part of the Earth's liquid core seem to be affected by a stably stratified layer at the core–mantle boundary. Such a layer could have an observable signature in both long-term and short-term variations of the magnetic field of the Earth, which are used to probe the flow at the top of the core. Indeed, with the recent SWARM mission, it seems reasonable to be able to identify waves propagating in the core with period of several months, which may play an important role in the large-scale dynamics. In this paper, we characterize the influence of a stratified layer at the top of the core on deep quasi-geostrophic (Rossby) waves. We compute numerically the quasi-geostrophic eigenmodes of a rapidly rotating spherical shell, with a stably stratified layer near the outer boundary. Two simple models of stratification are taken into account, which are scaled with commonly adopted values of the Brunt–Väisälä frequency in the Earth's core. In the absence of magnetic field, we find that both azimuthal wavelength and frequency of the eigenmodes control their penetration into the stratified layer: the higher the phase speed, the higher the permeability of the stratified layer to the wave motion. We also show that the theory developed by Takehiro & Lister for thermal convection extends to the whole family of Rossby waves in the core. Adding a magnetic field, the penetrative behaviour of the quasi-geostrophic modes (the so-called fast branch) is insensitive to the imposed magnetic field and only weakly sensitive to the precise shape of the stratification. Based on these results, the large-scale and high-frequency modes (1–2 month periods) may be detectable in the geomagnetic data measured at the Earth's surface, especially in the equatorial area where the modes can be trapped.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 28
    Publication Date: 2015-08-16
    Description: A number of factors influence the performance of an ejector, e.g. working fluid, geometry and operating conditions. In the present work, six low-environmental-impact working fluids were evaluated for their use in an ejector cooling system running on low-temperature thermal energy. The numerical analysis was based on a model applying the 1D constant-pressure mixing theory. Ejector performance was assessed for the temperatures of the generator, evaporator and condenser in the range of 80–120°C, 5–15°C and 25–40°C, respectively. The results indicated that owing to its high coefficient of performance and moderate operating pressures throughout the entire ejector cycle, isobutane is a good choice for a refrigerant. The area ratio required for running the ejector in critical mode, under changing operating conditions, varied in a significant range regardless of the selected refrigerant. This clearly indicates the importance of a variable geometry ejector design to strengthen the position of ejector cooling systems among other refrigeration technologies.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 29
    Publication Date: 2015-08-16
    Description: The thermal performance of a disc-shaped heat generation body with cooling channels is investigated by using constructal theory based on previous model of heat convection on a disc and previous analytical method of heat conduction on a disc. By taking minimum dimensionless maximum thermal resistance as optimization objective, the optimal aspect ratio of the elemental sector in the radial-pattern disc is obtained for the specified power pumping of the elemental sector; the optimal width ratio of the first-order and elemental cooling channels and the optimal dimensionless radius of the elemental sector are obtained for the specified power pumping of the disc. There exists a critical radius of the disc to determine whether the radial-pattern design and branched-pattern design should be adopted. These conclusions are different from those obtained by Wechsatol et al. 's model, and the essential reason for these differences is that the power pumping is specified in this article, but not the specified flow rate number in Wechsatol et al. 's model. Finally, the assumption about the heat capacity of the coolant and the thermal conductivity of the disc is validated. An analytical method is introduced in this article, which can provide another thought for the constructal optimization of disc with heat convection. The optimal constructs of the discs are obtained for the specified power pumping, which provides some different guidelines for the design of disc with heat convection.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 30
    Publication Date: 2015-08-16
    Description: Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 31
    Publication Date: 2015-08-16
    Description: In the present paper, design of solar chimney (SC) and earth-to-air heat exchanger (EAHE) to meet the thermal need of flat buildings are studied regarding adaptive thermal comfort criteria. Investigation on the effects of geometric features shows that the design of SC with the air gap and outlet sizes of 0.2 m and also EAHE with the diameter and length of 0.5 and 25.0 m reveals better performance. Thermal comfort analysis shows that the SC is capable to power the underground heating system during few hours of the sunny days even at the ambient temperature as low as 0°C and the heating demand of 1000 W without needing the auxiliary devices. In addition, the required numbers of SCs and the underground air channels are strongly influenced by environmental outdoor conditions and heating demand of building and are approximately calculated by: $$\hbox{ room }\phantom{\rule{0.08em}{0ex}}\hbox{ volume/50 }\phantom{\rule{0.08em}{0ex}}\hbox{ and }\phantom{\rule{0.08em}{0ex}}\hbox{ 2 }\times (\hbox{ room }\phantom{\rule{0.08em}{0ex}}\hbox{ volume/50 })+\hbox{ 1, }$$ respectively.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 32
    Publication Date: 2015-09-19
    Description: Sequence alignment is a long standing problem in bioinformatics. The Basic Local Alignment Search Tool (BLAST) is one of the most popular and fundamental alignment tools. The explosive growth of biological sequences calls for speedup of sequence alignment tools such as BLAST. To this end, we develop high speed BLASTN (HS-BLASTN), a parallel and fast nucleotide database search tool that accelerates MegaBLAST—the default module of NCBI-BLASTN. HS-BLASTN builds a new lookup table using the FMD-index of the database and employs an accurate and effective seeding method to find short stretches of identities (called seeds) between the query and the database. HS-BLASTN produces the same alignment results as MegaBLAST and its computational speed is much faster than MegaBLAST. Specifically, our experiments conducted on a 12-core server show that HS-BLASTN can be 22 times faster than MegaBLAST and exhibits better parallel performance than MegaBLAST. HS-BLASTN is written in C++ and the related source code is available at https://github.com/chenying2016/queries under the GPLv3 license.
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 33
    Publication Date: 2015-05-29
    Description: Model evaluation is a necessary step for better prediction and design of 3D RNA structures. For proteins, this has been widely studied and the knowledge-based statistical potential has been proved to be one of effective ways to solve this problem. Currently, a few knowledge-based statistical potentials have also been proposed to evaluate predicted models of RNA tertiary structures. The benchmark tests showed that they can identify the native structures effectively but further improvements are needed to identify near-native structures and those with non-canonical base pairs. Here, we present a novel knowledge-based potential, 3dRNAscore, which combines distance-dependent and dihedral-dependent energies. The benchmarks on different testing datasets all show that 3dRNAscore are more efficient than existing evaluation methods in recognizing native state from a pool of near-native states of RNAs as well as in ranking near-native states of RNA models.
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 34
    Publication Date: 2015-05-31
    Description: A 3-D magnetotelluric (MT) inversion code using unstructured tetrahedral elements has been developed in order to correct the topographic effect by directly incorporating it into computational grids. The electromagnetic field and response functions get distorted at the observation sites of MT surveys because of the undulating surface topography, and without correcting this distortion, the subsurface structure can be misinterpreted. Of the two methods proposed to correct the topographic effect, the method incorporating topography explicitly in the inversion is applicable to a wider range of surveys. For forward problems, it has been shown that the finite element method using unstructured tetrahedral elements is useful for the incorporation of topography. Therefore, this paper shows the applicability of unstructured tetrahedral elements in MT inversion using the newly developed code. The inversion code is capable of using the impedance tensor, the vertical magnetic transfer function (VMTF), and the phase tensor as observational data, and it estimates the subsurface resistivity values and the distortion tensor of each observation site. The forward part of the code was verified using two test models, one incorporating topographic effect and one without, and the verifications showed that the results were almost the same as those of previous works. The developed inversion code was then applied to synthetic data from a MT survey, and was verified as being able to recover the resistivity structure as well as other inversion codes. Finally, to confirm its applicability to the data affected by topography, inversion was performed using the synthetic data of the model that included two overlapping mountains. In each of the cases using the impedance tensor, the VMTF and the phase tensor, by including the topography in the mesh, the subsurface resistivity was determined more proficiently than in the case using the flat-surface mesh. Although the locations of the anomalies were not accurately estimated by the inversion using distorted impedance tensors due to the slightly undervalued gain, these locations were correctly estimated by using undistorted impedance tensors or adding VMTFs in the data. Therefore, it can be concluded that the inversion using the unstructured tetrahedral element effectively prevents the misinterpretation of subsurface resistivity and recovers subsurface resistivity proficiently by representing the topography in the computational mesh.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 35
    Publication Date: 2015-05-31
    Description: Separating the contribution of different hematite coercivity grains to the magnetic fabric is a standing problem in rock magnetism because of the common occurrence of thermochemical alterations when measuring the anisotropy of thermal remanence. A technique that eliminates this bias is presented, which is useful when there is a need to separate the fabric of detrital from pigmentary hematite, for example. The method is based on stepwise thermal demagnetization of saturation isothermal remanent magnetizations (IRMs) applied orthogonally on three sister specimens, allowing calculation of the anisotropy tensor from the three components of each demagnetized IRM vector, avoiding the necessity of having to apply IRMs to thermochemically altered specimens. Vector subtraction allows determining the anisotropy tensor for specific unblocking-temperature ranges. The anisotropies of the pigmentary, specular and total hematite of the Mauch Chunk Formation red beds of Pennsylvania have been measured from an oriented block sample and results are compared to previous anisotropy measurements performed using the high-field anisotropy of isothermal remanence technique (hf-AIR), which measures total undifferentiated hematite. Experiments were conducted using non-saturating 1 T and fully saturating 5.5 T fields: both experimental sets seem capable of measuring the orientation of the specularite anisotropy principal axes, but 5.5 T are needed to capture the orientation of the higher coercivity pigmentary grains. The magnitudes of the principal axes, instead, are only faithfully measured using 5.5 T fields and yield somewhat higher anisotropies than those measured by hf-AIR. The fundamental requirement for this technique is homogeneous material among the three sister specimens, which is a significant limitation; homogeneity tests allow assessment of applicability of the method and reliability of the results.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 36
    Publication Date: 2016-07-29
    Description: Archaeomagnetic field models cover longer timescales than historical models and may therefore resolve the motion of geomagnetic features on the core–mantle boundary (CMB) in a more meaningful statistical sense. Here we perform a detailed appraisal of archaeomagnetic field models to infer some aspects of the physics of the outer core. We characterize and compare the identification and tracking of reversed flux patches (RFPs) in order to assess the RFPs robustness. We find similar behaviour within a family of models but differences among different families, suggesting that modelling strategy is more influential than data set. Similarities involve recurrent positions of RFPs, but no preferred direction of motion is found. The tracking of normal flux patches shows similar qualitative behaviour confirming that RFPs identification and tracking is not strongly biased by their relative weakness. We also compare the tracking of RFPs with that of the historical field model gufm1 and with seismic anomalies of the lowermost mantle to explore the possibility that RFPs have preferred locations prescribed by lower mantle lateral heterogeneity. The archaeomagnetic field model that most resembles the historical field is interpreted in terms of core dynamics and core–mantle thermal interactions. This model exhibits correlation between RFPs and low seismic shear velocity in co-latitude and a shift in longitude. These results shed light on core processes, in particular we infer toroidal field lines with azimuthal orientation below the CMB and large fluid upwelling structures with a width of about 80° (Africa) and 110° (Pacific) at the top of the core. Finally, similar preferred locations of RFPs in the past 9 and 3 kyr of the same archaeomagnetic field model suggest that a 3 kyr period is sufficiently long to reliably detect mantle control on core dynamics. This allows estimating an upper bound of 220–310 km for the magnetic boundary layer thickness below the CMB.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 37
    Publication Date: 2016-07-16
    Description: Post-depositional reductive diagenesis usually results in partial or entire cleansing of the pristine palaeomagnetic signal, therefore, its intensity is important to be assessed for sediments that are in the purpose of retrieving palaeomagnetic information. Grain size, rock magnetic and geochemical studies on the entire core, along with scanning electron microscope observations and X-ray diffraction analyses for representative samples were carried out on a Holocene sediment core retrieved from the deep water part of Huguangyan maar lake (HGY), southeast China. The pristine magnetic mineral assemblage of the studied core is domianted by superparamagnetic (SP) and stable single domain titanomagnetite, and high coercivity minerals are not detectable. Based on down-core variations of the average grain size ( M Z ), total organic carbon (TOC), detrital elements (Al, Ti, Fe and Mn) and the concentration and mineralogy of magnetic minerals, the studied core could be divided into three subsections. The uppermost subsection is the least affected by diagenesis, with detrital titanomagnetite as the dominant magnetic mineral. This is owing to low TOC contents, but high detrital input generated by weak Asian summer monsoon intensity during the late Holocene. The intermediate subsection shows down-core progressively enhanced dissolution of detrital titanomagnetite, and concomitant formation of authigenic pyrite and siderite, which indicates down-core progressively enhanced diagenesis generated by down-core progressive increasing TOC content, but decreasing detrital input as the result of down-core progressively strengthened Asian summer monsoon intensity. The pristine magnetic mineral assemblage has been profoundly modified in the lowermost subsection. At certain positions of the lowermost subsection, detrital titanomagnetite has been even completely dissolved via diagenesis, giving place to authigenic pyrite and siderite. High TOC content, but low detrital input generated from strong Asian summer monsoon intensity during the early Holocene are accountable for intensive diagenesis in the lowermost subsection. Complete erasing of detrital magnetic input signal at certain positions of the lowermost subsection, and considerable formation of authigenic siderite indicate that palaeomagnetic records of the studied core have been significantly compromised. The studied core has relatively higher TOC content, lower detrital matter content, calmer sedimentary environments, and less DO available at its water–sediment interface than the cores retrieved at relatively shallower water depths, which all contribute to its relatively stronger diagenesis. Progressive thickening of the upper two subsections with increasing water depth is owing to progressive increase in sedimentation rate with increasing water depth, which is the key factor in determining the thickness of each diagenetic subsection of cores from HGY. It would be better that lake sediments for palaeomagnetic investigations collected at a water depth shallower than the depth of its thermocline.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 38
    Publication Date: 2016-06-21
    Description: The goal of pathway analysis is to identify the pathways that are significantly impacted when a biological system is perturbed, e.g. by a disease or drug. Current methods treat pathways as independent entities. However, many signals are constantly sent from one pathway to another, essentially linking all pathways into a global, system-wide complex. In this work, we propose a set of three pathway analysis methods based on the impact analysis, that performs a system-level analysis by considering all signals between pathways, as well as their overlaps. Briefly, the global system is modeled in two ways: (i) considering the inter-pathway interaction exchange for each individual pathways, and (ii) combining all individual pathways to form a global, system-wide graph. The third analysis method is a hybrid of these two models. The new methods were compared with DAVID, GSEA, GSA, PathNet, Crosstalk and SPIA on 23 GEO data sets involving 19 tissues investigated in 12 conditions. The results show that both the ranking and the P -values of the target pathways are substantially improved when the analysis considers the system-wide dependencies and interactions between pathways.
    Keywords: Computational Methods
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  • 39
    Publication Date: 2016-05-05
    Description: The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In this study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modelling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 40
    Publication Date: 2016-05-06
    Description: Several works have reported that haematite has non-linear initial susceptibility at room temperature, like pyrrhotite or titanomagnetite, but there is no explanation for the observed behaviours yet. This study sets out to determine which physical property (grain size, foreign cations content and domain walls displacements) controls the initial susceptibility. The performed measurements include microprobe analysis to determine magnetic phases different to haematite; initial susceptibility (300 K); hysteresis loops, SIRM and backfield curves at 77 and 300 K to calculate magnetic parameters and minor loops at 77 K, to analyse initial susceptibility and magnetization behaviours below Morin transition. The magnetic moment study at low temperature is completed with measurements of zero field cooled–field cooled and AC susceptibility in a range from 5 to 300 K. The minor loops show that the non-linearity of initial susceptibility is closely related to Barkhausen jumps. Because of initial magnetic susceptibility is controlled by domain structure it is difficult to establish a mathematical model to separate magnetic subfabrics in haematite-bearing rocks.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 41
    Publication Date: 2016-07-09
    Description: Bioinformatic analysis often produces large sets of genomic ranges that can be difficult to interpret in the absence of genomic context. Goldmine annotates genomic ranges from any source with gene model and feature contexts to facilitate global descriptions and candidate loci discovery. We demonstrate the value of genomic context by using Goldmine to elucidate context dynamics in transcription factor binding and to reveal differentially methylated regions (DMRs) with context-specific functional correlations. The open source R package and documentation for Goldmine are available at http://jeffbhasin.github.io/goldmine .
    Keywords: Computational Methods
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  • 42
    Publication Date: 2016-07-28
    Description: CCCTC-binding factor (CTCF) is a multi-functional protein that is assigned various, even contradictory roles in the genome. High-throughput sequencing-based technologies such as ChIP-seq and Hi-C provided us the opportunity to assess the multivalent functions of CTCF in the human genome. The location of CTCF-binding sites with respect to genomic features provides insights into the possible roles of this protein. Here we present the first genome-wide survey and characterization of three important functions of CTCF: enhancer insulator, chromatin barrier and enhancer linker. We developed a novel computational framework to discover the multivalent functions of CTCF based on chromatin state and three-dimensional chromatin architecture. We applied our method to five human cell lines and identified ~46 000 non-redundant CTCF sites related to the three functions. Disparate effects of these functions on gene expression were found and distinct genomic features of these CTCF sites were characterized in GM12878 cells. Finally, we investigated the cell-type specificities of CTCF sites related to these functions across five cell types. Our study provides new insights into the multivalent functions of CTCF in the human genome.
    Keywords: Computational Methods
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  • 43
    Publication Date: 2016-07-29
    Description: A series of important geological events occurred in the Tibetan Plateau area during the Jurassic, such as the collision of the Lhasa and Qiangtang Terranes, the closure of the Meso-Tethyan Ocean, the opening of the Neo-Tethyan Ocean and the cessation of the mega-monsoon. The ~3000 m thick Jurassic sedimentary sequence in the Qiangtang Basin on the central Tibetan Plateau, which is called the Yanshiping (YSP) Group, recorded these geological events. However, the chronology of the sequence is surprisingly poorly constrained. Here, we perform a detailed palaeomagnetic analysis on the ~1060 m thick middle and upper portions of the YSP Group (the Xiali and Suowa Formations) in the YSP section of the eastern Qiangtang Basin. Three bivalve zones at stratigraphic intervals of ~40–140, 640–800 and 940–1040 m are identified, which yield a Bathonian–Callovian age for the Lower Xiali Fm., a Callovian–Oxfordian age for the Lower Suowa Fm. and an Oxfordian–Kimmeridgian age for the Upper Suowa Fm. A total of 544 oriented palaeomagnetic samples were collected from the section. By combining thermal and alternating field demagnetizations, clear characteristic remanent magnetization (ChRM) directions are isolated for most of the samples. The robust ChRM directions pass fold and reversals tests, which support the primary nature of the ChRMs and yield a palaeopole at 76.8°N/297.2°E (dp = 2.2°, dm = 3.7°). A total of 27 normal and 26 reversed polarity zones were successfully recorded in the section. Combined with fossil age constraints, results suggest that the section is plausibly composed of a Callovian-Early Kimmeridgian age sedimentary sequence.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 44
    Publication Date: 2015-05-03
    Description: This study investigates pressure effects on the magnetic properties of non-interacting single-domain (SD) magnetite. Using a high-pressure cell specially designed for a Magnetic Property Measurement System, magnetic hysteresis measurements were conducted under high pressures of up to 1 GPa on natural plagioclase crystals containing much acicular SD magnetite. Coercivity and saturation magnetization were nearly constant with pressure, while saturation remanent magnetization and coercivity of remanence decreased with pressure at moderate rates of –8 per cent GPa –1 and –18 per cent GPa –1 , respectively. These results suggest that temperature effects govern the magnetic behaviour of acicular SD magnetite grains in the middle and lower crusts.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 45
    Publication Date: 2015-05-03
    Description: MicroRNAs (miRNAs) regulate gene expression by binding to partially complementary sequences on target mRNA transcripts, thereby causing their degradation, deadenylation, or inhibiting their translation. Genomic variants can alter miRNA regulation by modifying miRNA target sites, and multiple human disease phenotypes have been linked to such miRNA target site variants (miR-TSVs). However, systematic genome-wide identification of functional miR-TSVs is difficult due to high false positive rates; functional miRNA recognition sequences can be as short as six nucleotides, with the human genome encoding thousands of miRNAs. Furthermore, while large-scale clinical genomic data sets are becoming increasingly commonplace, existing miR-TSV prediction methods are not designed to analyze these data. Here, we present an open-source tool called SubmiRine that is designed to perform efficient miR-TSV prediction systematically on variants identified in novel clinical genomic data sets. Most importantly, SubmiRine allows for the prioritization of predicted miR-TSVs according to their relative probability of being functional. We present the results of SubmiRine using integrated clinical genomic data from a large-scale cohort study on chronic obstructive pulmonary disease (COPD), making a number of high-scoring, novel miR-TSV predictions. We also demonstrate SubmiRine's ability to predict and prioritize known miR-TSVs that have undergone experimental validation in previous studies.
    Keywords: Computational Methods
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  • 46
    Publication Date: 2015-05-07
    Description: Characterization of geomagnetic field behaviour on timescales of centuries to millennia is necessary to understand the mechanisms that sustain the geodynamo and drive its evolution. As Holocene paleomagnetic and archeomagnetic data have become more abundant, strategies for regularized inversion of modern field data have been adapted to produce numerous time-varying global field models. We evaluate the effectiveness of several approaches to inversion and data handling, by assessing both global and regional properties of the resulting models. Global Holocene field models cannot resolve Southern hemisphere regional field variations without the use of sediments. A standard data set is used to construct multiple models using two different strategies for relative paleointensity calibration and declination orientation and a selection of starting models in the inversion procedure. When data uncertainties are considered, the results are similar overall regardless of whether we use iterative calibration and reorientation, or co-estimation of the calibration and orientation parameters as part of the inversion procedure. In each case the quality of the starting model used for initial relative paleointensity calibration and declination orientation is crucial and must be based on the best absolute information available. Without adequate initial calibration the morphology of dipole moment variations can be recovered but its absolute value will be correlated with the initial intensity calibrations, an effect that might be mitigated by ensuring an appropriate fit to enough high quality absolute intensity data with low uncertainties. The declination reorientation mainly impacts regional field structure and in the presence of non-zonal fields will result in a non-zero local average. The importance of declination orientation is highlighted by inconsistencies in the West Pacific and Australian sediment records in CALS10k.1b model. Great care must also be taken to assess uncertainties associated with both paleomagnetic and age data and to evaluate the effects of poor data distribution. New consistently allocated uncertainty estimates for sediment paleomagnetic records highlight the importance of adequate uncertainties in the inversion process, as they determine the relative weighting among the data and overall normalized misfit levels which in turn influence the complexity of the inferred field models. Residual distributions suggest that the most appropriate misfit measure is the L 1 norm (minimum absolute deviation) rather than L 2 (least squares), but this seems to have relatively minor impact on the overall results. For future Holocene field modelling we see a need for comprehensive methods to assess uncertainty in individual archeomagnetic data so that these data or models derived from them can be used for reliable initial relative paleointensity calibration and declination orientation in sediments. More work will be needed to assess whether co-estimation or an iterative approach to inversion is more efficient overall. This would be facilitated by realistic and globally consistent data and age uncertainties from the paleomagnetic community.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 47
    Publication Date: 2015-05-16
    Description: Galvanic distortion of magnetotelluric (MT) data due to small-scale surficial bodies or due to topography is one of the major factors that prevents accurate imaging of the subsurface. We present a 3-D algorithm for joint inversion of MT impedance tensor data and a frequency-independent full distortion matrix that circumvents this problem. We perform several tests of our algorithm on synthetic data affected by different amounts of distortion. These tests show that joint inversion leads to a better conductivity model compared to the inversion of the MT impedance tensor without any correction for distortion effects. For highly distorted data, inversion without any distortion correction results in strong artefacts and we cannot fit the data to the specified noise level. When the distortion is reduced, we can fit the data to an RMS of one, but still observe artefacts in the shallow part of the model. In contrast, in both cases our joint inversion can fit the data within the assumed noise level and the resulting models are comparable to the inversion of undistorted data. In addition, we show that the elements of the full distortion matrix can be well resolved by our algorithm. Finally, when inverting undistorted data, including the distortion matrix in the inversion only results in a minor loss of resolution. We therefore consider our new approach a promising tool for the general analysis of field MT data.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 48
    Publication Date: 2015-05-13
    Description: In the last decade, interest in heat storage systems has been increasing. These systems will have increasing importance for utilization of solar energy in domestic heating systems. As solar energy is a diurnal cyclic resource, storing excess solar energy for long- or short-term periods will both increase the utilization of solar energy systems and decrease fossil fuel consumption. The relatively new heat storage method using thermochemical storage has shown some significant advantages such as low heat loss (-〉 zero), high heat storage density and low space requirement. These important properties make thermochemical storage a promising alternative for long-term energy storage. In the present study, a numerical investigation on ‘open’ seasonal thermochemical storage has been undertaken. The simulation results show that the volume/mass of the absorbent, mass flow rate and relative humidity of air have significant importance on the reaction kinetics and system performance during the system discharging process. Conversely, total collector area, solar radiation and mass flow rate of air are important parameters during the charging process. The results conclude that, overall, reactor design is the most important factor for storage performance. In addition, reaction advancement ( X ) has a significant importance on process efficiency.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
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  • 49
    Publication Date: 2015-05-13
    Description: Photovoltaic (PV) combined with phase change material (PV/PCM) system is a hybrid solar system that uses a PCM to reduce the PV temperature and to store energy for other applications. This study aims to increase the integrated PV efficiency of buildings by incorporating PCM while utilizing the stored heat in PCM for controlling indoor conditions. Experiments have been carried out on a prototype PV/PCM air system using monocrystalline PV modules. Transient simulations of the system performance have also been performed using a commercial computational fluid dynamics package based on the finite volume method. The results from simulation were validated by comparing it with experimental results. The results indicate that PCM is effective in limiting temperature rise in PV device and the heat from PCM can enhance night ventilation and decrease the building energy consumption to achieve indoor thermal comfort for certain periods of time.
    Keywords: Other low-carbon energy technologies
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  • 50
    Publication Date: 2015-05-13
    Description: Heat pipes and thermosyphons—devices of high effective thermal conductivity—have been studied for many years for enhancing the performance of solid, liquid and phase change material (PCM) heat stores. However, as the applications of heat storage widen, from micro-electronics thermal control to concentrated solar heat storage and vehicle thermal management, and even for chemical reactor isothermalization, the challenges facing heat storage increasingly are moving from those associated with the ‘standard’ diurnal storage, in itself a problem for low thermal conductivity materials, to response times measured in a few hours or even minutes. While high thermal conductivity metals such as foams can be impregnated with a PCM, for example, to increase local conductivity, the rapid heat input and removal necessitates a more radical approach—heat pipes, possibly with feedback control, with innovative PCM interfaces. This paper reviews the use of heat pipes in conventional and rapid response PCM and liquid or cold storage applications and introduces some novel concepts that might overcome current limitations.
    Keywords: Other low-carbon energy technologies
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  • 51
    Publication Date: 2015-05-13
    Description: The effect of different charging infrastructure configurations on the electric-driven distance of plug-in hybrid electric vehicles (e-mileage) has been investigated, using an agent-based traffic simulation. Our findings suggest that the same e-mileage can be achieved with fewer charging poles if the poles support charging from several parking slots around them, and the charging cable is switched from one vehicle to the next. We also find that the charging power supported by most Finnish charging stations, 3.7 kW, and the cable switching delay of 1 h seem to be sufficient for effective workplace charging.
    Keywords: Other low-carbon energy technologies
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  • 52
    Publication Date: 2015-05-16
    Description: The magnetic field that originates in the earth's core is transformed across the electrically conducting mantle before being observed, at the earth's surface or above. Assuming that the conductivity depends only on radius, it has been customary to treat the mantle as a linear time-invariant filter for the core magnetic field, with properties (as a function of the frequency ) specified by the transfer function (). An high-frequency approximation to (), which is derived from a three terms WKBJ expansion with –1/2 as small parameter, is found here to reproduce adequately, for low harmonic degrees and/or thin conducting layers, the exact solution, which is evaluated numerically. It is contrasted with the low-frequency estimation of , which consists in a perturbation procedure and in writing () as a series in powers of ( -〉 0). The low-frequency theory is applied to the magnetic variations produced by the geostrophic core flows with about 6 yr period as the phase of these flows is independently determined from their effect on the length of the day. Apart from that, the low-frequency approximation overestimates the screening by the mantle of high-frequency signals, especially the low harmonic degree ones. In practice, the attenuating factor defined from the O ( 2 ) term in the expansion of as -〉 0 cannot be retrieved from analyses of geomagnetic time-series. Application of the mantle filter theory hinges on our knowledge about the time spectrum of the magnetic field at the core surface. The low-frequency theory had been previously applied to observatory series on the assumption that geomagnetic jerks occurring in the core are rare and isolated events. Rather than following up these earlier studies, I note that the spectral density function for the second time derivative of the main magnetic field coefficients is approximately independent of in a frequency range for which the mantle has undoubtedly negligible influence. In the absence of any other information, this scaling law is extrapolated to higher frequencies.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 53
    Publication Date: 2015-01-24
    Description: Of the ~1.3 million Alu elements in the human genome, only a tiny number are estimated to be active in transcription by RNA polymerase (Pol) III. Tracing the individual loci from which Alu transcripts originate is complicated by their highly repetitive nature. By exploiting RNA-Seq data sets and unique Alu DNA sequences, we devised a bioinformatic pipeline allowing us to identify Pol III-dependent transcripts of individual Alu elements. When applied to ENCODE transcriptomes of seven human cell lines, this search strategy identified ~1300 Alu loci corresponding to detectable transcripts, with ~120 of them expressed in at least three cell lines. In vitro transcription of selected Alu s did not reflect their in vivo expression properties, and required the native 5'-flanking region in addition to internal promoter. We also identified a cluster of expressed Alu Ya5-derived transcription units, juxtaposed to snaR genes on chromosome 19, formed by a promoter-containing left monomer fused to an Alu -unrelated downstream moiety. Autonomous Pol III transcription was also revealed for Alu s nested within Pol II-transcribed genes. The ability to investigate Alu transcriptomes at single-locus resolution will facilitate both the identification of novel biologically relevant Alu RNAs and the assessment of Alu expression alteration under pathological conditions.
    Keywords: Computational Methods
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  • 54
    Publication Date: 2015-03-11
    Description: The magnetic field of the Earth's lithosphere arises from rock magnetization contrasts that were shaped over geological times. The field can be described mathematically in spherical harmonics or with distributions of magnetization. We exploit this dual representation and assume that the lithospheric field is induced by spatially varying susceptibility values within a shell of constant thickness. By introducing a statistical assumption about the power spectrum of the susceptibility, we then derive a statistical expression for the spatial power spectrum of the crustal magnetic field for the spatial scales ranging from 60 to 2500 km. This expression depends on the mean induced magnetization, the thickness of the shell, and a power law exponent for the power spectrum of the susceptibility. We test the relevance of this form with a misfit analysis to the observational NGDC-720 lithospheric magnetic field model power spectrum. This allows us to estimate a mean global apparent induced magnetization value between 0.3 and 0.6 A m –1 , a mean magnetic crustal thickness value between 23 and 30 km, and a root mean square for the field value between 190 and 205 nT at 95 per cent. These estimates are in good agreement with independent models of the crustal magnetization and of the seismic crustal thickness. We carry out the same analysis in the continental and oceanic domains separately. We complement the misfit analyses with a Kolmogorov–Smirnov goodness-of-fit test and we conclude that the observed power spectrum can be each time a sample of the statistical one.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 55
    Publication Date: 2016-04-07
    Description: Data on the evolution of Earth's magnetic field intensity are important for understanding the geodynamo and planetary evolution. However, the paleomagnetic record in rocks may be adversely affected by many physical processes, which must be taken into account when analysing the palaeointensity database. This is especially important in the light of an ongoing debate regarding core thermal conductivity values, and how these relate to the Precambrian geodynamo. Here, we demonstrate that several data sets in the Precambrian palaeointensity database overestimate the true paleofield strength due to the presence of non-ideal carriers of palaeointensity signals and/or viscous re-magnetizations. When the palaeointensity overestimates are removed, the Precambrian database does not indicate a robust change in geomagnetic field intensity during the Mesoproterozoic. These findings call into question the recent claim that the solid inner core formed in the Mesoproterozoic, hence constraining the thermal conductivity in the core to ‘moderate’ values. Instead, our analyses indicate that the presently available palaeointensity data are insufficient in number and quality to constrain the timing of solid inner core formation, or the outstanding problem of core thermal conductivity. Very young or very old inner core ages (and attendant high or low core thermal conductivity values) are consistent with the presently known history of Earth's field strength. More promising available data sets that reflect long-term core structure are geomagnetic reversal rate and field morphology. The latter suggests changes that may reflect differences in Archean to Proterozoic core stratification, whereas the former suggest an interval of geodynamo hyperactivity at ca. 550 Ma.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 56
    Publication Date: 2016-04-08
    Description: Existing methods for interpreting protein variation focus on annotating mutation pathogenicity rather than detailed interpretation of variant deleteriousness and frequently use only sequence-based or structure-based information. We present VIPUR, a computational framework that seamlessly integrates sequence analysis and structural modelling (using the Rosetta protein modelling suite) to identify and interpret deleterious protein variants. To train VIPUR, we collected 9477 protein variants with known effects on protein function from multiple organisms and curated structural models for each variant from crystal structures and homology models. VIPUR can be applied to mutations in any organism's proteome with improved generalized accuracy (AUROC .83) and interpretability (AUPR .87) compared to other methods. We demonstrate that VIPUR's predictions of deleteriousness match the biological phenotypes in ClinVar and provide a clear ranking of prediction confidence. We use VIPUR to interpret known mutations associated with inflammation and diabetes, demonstrating the structural diversity of disrupted functional sites and improved interpretation of mutations associated with human diseases. Lastly, we demonstrate VIPUR's ability to highlight candidate variants associated with human diseases by applying VIPUR to de novo variants associated with autism spectrum disorders.
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 57
    Publication Date: 2016-01-11
    Description: Red Clay underlying the loess-palaeosol sequences on the Chinese Loess Plateau is an eolian deposit. There is a controversy over whether magnetic susceptibility ( ) variations in Red Clay sequence can be used as an indicator of summer palaeomonsoon intensity. This study investigates the magnetic mineralogy, magnetic concentration and magnetic grain size distribution of Jiaxian Red Clay with multimagnetic methods. Our results indicate that the magnetic properties of Jiaxian Red Clay are similar to those of the Quaternary loess-palaeosol sequences, and ultrafine ferrimagnetic grains produced during pedogenesis are responsible for an increase in susceptibility, therefore the enhancement mechanism of Red Clay is similar to that of the overlying loess-palaeosol sequences. This paper explores variations in the Red Clay sequence through spatial and temporal analysis. The susceptibility variation of six sites along a NNE to SSW transect correlate to palaeoclimatic cycles, so can be used to trace the summer palaeomonsoon intensity from a spatial perspective. However, a simple loess-derived calibration function cannot be used to quantitative reconstruct the palaeomonsoon intensity variations thought time. An adjusted calibration function for palaeosols from Red Clay sequence needs to be developed, so that can be used to quantitative reconstruct palaeomonsoon intensity. Further study is necessary to develop such a transfer function.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 58
    Publication Date: 2016-03-09
    Description: Palaeointensity experiments were carried out to a sample collection from two sections of basalt lava flow sequences of Pliocene age in north central Iceland (Chron C2An) to further refine the knowledge of the behaviour of the palaeomagnetic field. Selection of samples was mainly based on their stability of remanence to thermal demagnetization as well as good reversibility in variations of magnetic susceptibility and saturation magnetization with temperature, which would indicate the presence of magnetite as a product of deuteric oxidation of titanomagnetite. Among 167 lava flows from two sections, 44 flows were selected for the Königsberger–Thellier–Thellier experiment in vacuum. In spite of careful pre-selection of samples, an Arai plot with two linear segments, or a concave-up appearance, was often encountered during the experiments. This non-ideal behaviour was probably caused by an irreversible change in the domain state of the magnetic grains of the pseudo-single-domain (PSD) range. This is assumed because an ideal linear plot was obtained in the second run of the palaeointensity experiment in which a laboratory thermoremanence acquired after the final step of the first run was used as a natural remanence. This experiment was conducted on six selected samples, and no clear difference between the magnetic grains of the experimented and pristine sister samples was found by scanning electron microscope and hysteresis measurements, that is, no occurrence of notable chemical/mineralogical alteration, suggesting that no change in the grain size distribution had occurred. Hence, the two-segment Arai plot was not caused by the reversible multidomain/PSD effect in which the curvature of the Arai plot is dependent on the grain size. Considering that the irreversible change in domain state must have affected data points at not only high temperatures but also low temperatures, f v ≥ 0.5 was adopted as one of the acceptance criteria where f v is a vectorially defined fraction of the linear segment. A measure of curvature k ' was also used to check the linearity of the selected linear segment. It was avoided, however, to reject the result out of hand by the large curvature k of the entire data points because it might still include a linear segment with a large fraction. Combining with the results of Shaw's experiments, 52 palaeointensities were obtained out of 192 specimens, or 11 flow means were obtained out of the 44 lava flows. Most of the palaeointensities were from the upper part of the lava section (Chron C2An.1n) and ranged between 30 and 66 μT. Including two results from the bottom part of the lava section, the mean virtual dipole moment for 2.5–3.5 Ma is 6.3 ± 1.4  x  10 22 Am 2 ( N  = 11), which is ~19 per cent smaller than the present-day dipole moment.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 59
    Publication Date: 2015-12-13
    Description: The sedimentary sequence deposited during the deglaciation phase following the last glacial maximum in the Storfjorden trough, on the northwestern Barents Sea south of Svalbard, was sampled with 10 piston and gravity cores during the SVAIS and EGLACOM cruises. Three cores (SV-02, SV-03 and SV-05) collected on the upper continental slope are characterized by a thin (20–40 cm) Holocene interval and a thick (up to 4.5 m in core SV-03) late Pleistocene sequence of finely laminated fine-grained sediments that have been interpreted as plumites deposited during the Melt Water Pulse 1a (MWP-1a). Radiocarbon ages obtained at the top and bottom of this stratigraphic interval revealed that deposition occurred during less than two centuries at around 15 ka ago, with a very high sedimentary rate exceeding 3 cm a –1 . We studied the palaeomagnetic and rock magnetic properties of this interval, by taking magnetic measurements at 1 cm spacing on u-channel samples collected from the three cores. The data show that this sequence is characterized by good palaeomagnetic properties and the palaeomagnetic and rock magnetic trends may be correlated at high resolution from core to core. The obtained palaeomagnetic data therefore offer the unique opportunity to investigate in detail the rate of geomagnetic palaeosecular variation (PSV) in the high northern latitudes at a decadal scale. Notwithstanding the palaeomagnetic trends of the three cores may be closely matched, the amplitude of directional PSV and the consequent virtual geomagnetic pole (VGP) scatter (S) is distinctly higher in one core (SV-05) than in the other two cores (SV-02 and SV-03). This might result from a variable proportion of two distinct populations of magnetic minerals in core SV-05, as suggested by the variable tendency to acquire a gyromagnetic remanent magnetization at high fields during the AF demagnetization treatment. For the plumite interval of cores SV-02 and SV-03, where the magnetic mineralogy is uniform and magnetite is the main magnetic carrier, a S value of about 9° is obtained. We consider this value as a reliable approximation of palaeomagnetic secular variation at a latitude of 75°N over a time interval spanning a couple of centuries around 15 ka ago.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 60
    Publication Date: 2015-12-13
    Description: A recent study of the Matuyama–Brunhes (M-B) geomagnetic field reversal recorded in exposed lacustrine sediments from the Sulmona Basin (Italy) provided a continuous, high-resolution record indicating that the reversal of the field direction at the terminus of the M-B boundary (MBB) occurred in less than a century, about 786 ka ago. In the sediment, thin (4–6 cm) remagnetized horizons were recognized above two distinct tephra layers—SUL2-19 and SUL2-20—that occur ~25 and ~35 cm below the MBB, respectively. Also, a faint, millimetre-thick tephra (SUL2-18) occurs 2–3 cm above the MBB. With the aim of improving the temporal resolution of the previous Sulmona MBB record and understanding the possible influence of cryptotephra on the M-B record in the Sulmona Basin, we performed more detailed sampling and analyses of overlapping standard and smaller samples from a 50 cm-long block that spans the MBB. The new data indicate that (i) the MBB is even sharper than previously reported and occurs ~2.5 cm below tephra SUL2-18, in agreement with the previous study; (ii) the MBB coincides with the rise of an intensity peak of the natural remanent magnetization (NRM) intensity, which extends across SUL2-18; (iii) except for a 2-cm-thick interval just above tephra SUL2-18, the rock magnetic parameters ( k , ARM, M r , M s , B c , B cr ) indicate exactly the same magnetic mineralogy throughout the sampled sequence. We conclude that either SUL2-18 resulted in the remagnetization of an interval of about 6 cm (i.e. during the NRM intensity peak spanning ~260 ± 110 yr, according to the estimated local sedimentation rate), and thus the detailed MBB record is lost because it is overprinted, or the MBB is well recorded, occurred abruptly about 2.5 cm below SUL2-18 and lasted less than 13 ± 6 yr. Both hypotheses challenge our understanding of the geomagnetic field behaviour during a polarity transition and/or of the NRM acquisition process in the Sulmona lacustrine sediment.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 61
    Publication Date: 2015-12-13
    Description: We test the ability of large-scale velocity fields inferred from geomagnetic secular variation data to produce the global magnetic field of the Earth. Our kinematic dynamo calculations use quasi-geostrophic (QG) flows inverted from geomagnetic field models which, as such, incorporate flow structures that are Earth-like and may be important for the geodynamo. Furthermore, the QG hypothesis allows straightforward prolongation of the flow from the core surface to the bulk. As expected from previous studies, we check that a simple QG flow is not able to sustain the magnetic field against ohmic decay. Additional complexity is then introduced in the flow, inspired by the action of the Lorentz force. Indeed, on centennial timescales, the Lorentz force can balance the Coriolis force and strict quasi-geostrophy may not be the best ansatz. When our columnar flow is modified to account for the action of the Lorentz force, magnetic field is generated for Elsasser numbers larger than 0.25 and magnetic Reynolds numbers larger than 100. This suggests that our large-scale flow captures the relevant features for the generation of the Earth's magnetic field and that the invisible small-scale flow may not be directly involved in this process. Near the threshold, the resulting magnetic field is dominated by an axial dipole, with some reversed flux patches. Time dependence is also considered, derived from principal component analysis applied to the inverted flows. We find that time periods from 120 to 50 yr do not affect the mean growth rate of the kinematic dynamos. Finally, we note that the footprint of the inner core in the magnetic field generated deep in the bulk of the shell, although we did not include one in our computations.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
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    Topics: Geosciences
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  • 62
    Publication Date: 2015-12-13
    Description: The Auca Mahuida volcano (2.03–0.88 Ma) located east of the Andean thrust front in the Neuquén basin (Argentina) hosts an oil system of thermogenic origin and is affected by the NW–SE striking-faults. Intrusive bodies and the underlying Jurassic sediments constitute the reservoir rocks. Aeromagnetic data collected in the Auca Mahuida area detected multiple dipolar magnetic anomalies, many of which have reverse polarity. Palaeomagnetic measurements on rock samples collected in the field together with available age determinations indicate that the reversely magnetized sources were mainly emplaced during the Matuyama reverse polarity chron while the normal polarity sources were emplaced during the Olduvai and/or Jaramillo subchrons. The location and geometry of the intrusive bodies is poorly known and the customary magnetic inversion is rendered difficult because of multiple natural remanent magnetization directions. To address these difficulties, a voxel inversion was applied to model the vector residual magnetic intensity (VRMI) transformation of the observed total magnetic intensity data. The modelling showed a 1.5 km deep, subcircular ring-shaped intrusion below the summit of the volcano and a series of NW–SE elongated, fault-controlled intrusive bodies to depths up to 3–4 km. Our results show that magnetic data and VRMI modelling help resolve the geometry of the shallow plumbing system of volcanoes with remanently magnetized sources, and estimate the depth and geometry of potential oil reservoirs in volcanic areas.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 63
    Publication Date: 2015-08-29
    Description: Was the Yukon-Tanana Terrane (YTT), a California-sized part of south-central Yukon, an autochthonous or para-autochthonous part of northern British Columbia in the Early Cretaceous or was it part of a proposed allochthonous ‘Baja B.C.’ continent offshore of southern California? To answer this fundamental question, a paleomagnetic study has been completed on 347 specimens from 24 sites in the 114.7 ± 1.1 Ma Quiet Lake batholith. This 1300 km 2 pluton is composed mostly of massive medium-to-coarse grained biotite quartz monzonite that exhibits no evidence of either deformation or metamorphism, and that intrudes metamorphosed pre-Cretaceous basement rocks of the YTT in southern Yukon. The paleomagnetic analysis utilized thermal and alternating field step demagnetization, and saturation isothermal remanence methods. A well-defined characteristic remanent magnetization (ChRM) direction was isolated throughout the 500–585 °C temperature range at Decl. = 340.6°, Incl. = 77.4° ( N = 14 sites, k = 51.2, A 95 = 5.6°). The ChRM resides in magnetite with a low titanium content and is interpreted to be a primary thermoremanent magnetization. After correction for 490 km of geologically demonstrable dextral displacement on the inboard Tintina fault zone, the Quiet Lake batholith's paleopole is not significantly different at 95 per cent confidence from the co-eval 115 Ma reference paleopole for North America, giving non-significant translation and rotation estimates of 1.4° ± 5.1° (1) northwestwards and 10° ± 13° (1) clockwise, respectively. Thus, this is the first Early Cretaceous paleopole to show clearly that the YTT in Yukon is a para-autochthon that was part of North America's continental margin at that time. Further, after correction for Tintina fault displacement, the eight available Mesozoic YTT paleopoles agree closely with the North American apparent polar wander path (APWP). In contrast, the 22 paleopoles from the Intermontane Belt show the expected behaviour of an allochthonous thin-skin of terranes (i.e. ‘Baja B.C.’ behaviour) and record ~8° of northward translation and ~50° of clockwise rotation relative to both the YTT and North American APWPs during the Mesozoic and Paleogene.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 64
    Publication Date: 2015-10-22
    Description: There exists a fundamental as well as practical interest in being able to accurately forecast the future evolution of Earth's magnetic field at decadal to secular ranges. This work enables such forecasts by combining geomagnetic data with an Earth-like numerical model of a convection-driven fluid dynamo. The underlying data assimilation framework builds on recent progress in inverse geodynamo modelling, a method which estimates an internal dynamic structure for Earth's core from a snapshot of the magnetic field and its instantaneous rate of change at the surface, and takes advantage of linear relationships and long-range correlations between observed and hidden state variables. Here the method is further evolved into a single-epoch ensemble Kalman filter, in order to initialise at a given epoch an ensemble of states compatible with the observations and representative of the uncertainties in the estimation of hidden quantities. The ensemble dynamics, obtained by subsequent numerical integration of the prognostic model equations, are found to be governed by a thermal wind balance or equilibrium between buoyancy forces, the Coriolis force and the pressure gradient. The resulting core fluid flow pattern is a quasi-steady eccentric gyre organised in a column parallel to Earth's rotation axis, in equilibrium with a longitudinal hemispheric convective density anomaly pattern. The flow provides induction for the magnetic field, which also undergoes a realistic amount of diffusion. Predictions of the present magnetic field from data taken within the past century show that the ensemble has an average retaining good consistency with the true geomagnetic evolution and an acceptable spread well representative of prediction errors, up to at least a secular range. The predictability of the geodynamo thus appears to significantly exceed previous theoretical expectations based on the chaotic divergence of ensemble members. The assimilation generally outperforms the linear mathematical extrapolations from a 30-yr prediction range onwards, with a 40 per cent improvement in Earth-surface error at a secular range. The geomagnetic axial dipole decay observed over the past two centuries is predicted to continue at a similar pace in the next century, with a further loss of $1.1\pm 0.3 \hspace{2.84526pt}\mathrm{\mu T}$ by year 2115. The focal (or minimum intensity) point of the South Atlantic geomagnetic anomaly is predicted to enter the South Pacific region in the next century, with the anomaly itself further deepening and widening. By year 2065, the minimum intensity is predicted to decrease by $1.46\pm 0.4 \hspace{2.84526pt}\mathrm{\mu T}$ at the Earth surface and the focal point to move 12.8 ± 1.4 deg westwards with a slight northward component. This corresponds to a drift rate of 0.26 deg yr –1 , similar to the typical geomagnetic westward drift observed over the past four centuries. The same drift rate is also predicted until 2115 with a further (but more uncertain) intensity decrease.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 65
    Publication Date: 2016-07-03
    Description: Understanding the contribution of biogenic magnetic particles into sedimentary assemblages is a current challenge in palaeomagnetism. It has been demonstrated recently that magnetic particles produced through biologically controlled mineralization processes, such as magnetosomes from magnetotactic bacteria, contribute to the recording of natural remanent magnetization in marine and lacustrian sediments. Contributions from other, biologically induced, mineralization types, which are known from multiple laboratory experiments to include magnetic minerals, remain largely unknown. Here, we report magnetic properties of iron minerals formed by a community of iron- and manganese-reducing bacteria isolated from a natural groundwater deposit during a 2 yr long incubation experiment. The main iron phases of the biomineralized mass are lepidocrocite, goethite and magnetite, each of which has environmental significance. Unlike the majority of the previous studies that reported superparamagnetic grain size, and thus no remanence carrying capacity of biologically induced magnetite, hysteresis and first-order reversal curves measurements in our study have not detected significant superparamagnetic contribution. The biomineralized mass, instead, contains a mixture of single-domain to pseudo-single-domain and multidomain magnetite particles that are capable of carrying a stable chemical remanent magnetization. Isothermal remanent magnetization acquisition parameters and first-order reversal curves signatures of the biomineralized samples deviate from previously proposed criteria for the distinction of extracellular (biologically induced) magnetic particles in mixtures. Given its potential significance as a carrier of natural remanent magnetization, environmental requirements, distribution in nature and the efficiency in the geomagnetic field recording by biologically induced mineralization need comprehensive investigation.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 66
    Publication Date: 2016-08-26
    Description: Heat pipe heat exchangers could be employed as run-around coils in air conditioning systems for enhanced dehumidification and cooling. This article reviews some of the works conducted on the cooling and dehumidification aspects in various air conditioning systems. They have been proved to be effective in enhancing dehumidification and reducing air conditioning costs especially in hot and humid tropical countries.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 67
    Publication Date: 2016-08-26
    Description: The mitigation options to meet the ambitious carbon reduction targets set by the UK government are discussed in this paper, including the use of carbon capture and storage (CCS) technology, clean renewable energy integration and a proposed system of integrated fuel cell combined heat and power (FC-CHP) technology. Analysis shows that the use of CCS technology within the current infrastructure can abate half the electricity-associated CO 2 emissions; however, this comes at a high cost penalty. The emissions associated with domestic heat cannot be prevented without changes in the energy infrastructure. Hydrogen-powered fuel cells can provide clean energy at a range of scales and high efficiencies, especially when employed with a CHP system. However, production of CO 2 -free hydrogen is essential for fuel cell technology to contribute substantially to a low carbon economy globally. In this work, three methods were investigated for small-scale distributed hydrogen production, namely steam methane reforming, water electrolysis (WE) and cold plasma jet (CPJ). The criteria used for comparisons include the associated CO 2 emissions and the cost of energy production. CPJ decomposition of methane shows a high potential when combined with integrated FC-CHP technology for economically viable and CO 2 -free generation of energy, especially in comparison to WE. Including the value of the solid carbon product makes the plasma system most attractive economically.
    Keywords: Other low-carbon energy technologies
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  • 68
    Publication Date: 2016-08-25
    Description: Monthly means of the magnetic field measurements at ground observatories are a key data source for studying temporal changes of the core magnetic field. However, when they are calculated in the usual way, contributions of external (magnetospheric and ionospheric) origin may remain, which make them less favourable for studying the field generated by dynamo action in the core. We remove external field predictions, including a new way of characterizing the magnetospheric ring current, from the data and then calculate revised monthly means using robust methods. The geomagnetic secular variation (SV) is calculated as the first annual differences of these monthly means, which also removes the static crustal field. SV time-series based on revised monthly means are much less scattered than those calculated from ordinary monthly means, and their variances and correlations between components are smaller. On the annual to decadal timescale, the SV is generated primarily by advection in the fluid outer core. We demonstrate the utility of the revised monthly means by calculating models of the core surface advective flow between 1997 and 2013 directly from the SV data. One set of models assumes flow that is constant over three months; such models exhibit large and rapid temporal variations. For models of this type, less complex flows achieve the same fit to the SV derived from revised monthly means than those from ordinary monthly means. However, those obtained from ordinary monthly means are able to follow excursions in SV that are likely to be external field contamination rather than core signals. Having established that we can find models that fit the data adequately, we then assess how much temporal variability is required. Previous studies have suggested that the flow is consistent with torsional oscillations (TO), solid body-like oscillations of fluid on concentric cylinders with axes aligned along the Earth's rotation axis. TO have been proposed to explain decadal timescale changes in the length-of-day. We invert for flow models where the only temporal changes are consistent with TO, but such models have an unacceptably large data misfit. However, if we relax the TO constraint to allow a little more temporal variability, we can fit the data as well as with flows assumed constant over three months, demonstrating that rapid SV changes can be reproduced by rather small flow changes. Although the flow itself changes slowly, its time derivative can be locally (temporally and spatially) large, in particular when and where core surface secular acceleration peaks. Spherical harmonic expansion coefficients of the flows are not well resolved, and many of them are strongly correlated. Averaging functions, a measure of our ability to determine the flow at a given location from the data distribution available, are poor approximations to the ideal, even when centred on points of the core surface below areas of high observatory density. Both resolution and averaging functions are noticeably worse for the toroidal flow component, which dominates the flow, than the poloidal flow component, except around the magnetic equator where averaging functions for both components are poor.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 69
    Publication Date: 2016-08-26
    Description: A multistage continuous isothermal endoreversible chemical engine system with a finite driving fluid is investigated in this paper, and the mass transfer law obeys the linear mass transfer law [ $$g\propto \mathrm{\Delta }\mu $$ ]. Under the condition that both the initial time and the initial key component concentration in the driving fluid are fixed, the maximum power output of the multistage chemical engine system and the corresponding optimal concentration configuration of the key component in the driving fluid are derived by applying Hamilton–Jacobi–Bellman (HJB) theory, and numerical examples for three different boundary conditions are given. The results show that the difference between the chemical potential of the key component and the Carnot chemical potential for the maximum power output is a constant, and the key component concentration in the driving fluid decreases with the increase of time nonlinearly; when both the process period and the final concentration of the key component are fixed, there is an optimal control strategy for the maximum power output of the multistage chemical engine system, and the maximum power outputs of the system and the corresponding optimal control strategies are different for different final concentrations. The obtained results can provide some theoretical guidelines for the optimal designs and operations of practical energy conversion systems.
    Keywords: Other low-carbon energy technologies
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 70
    Publication Date: 2016-08-26
    Description: Recently, several studies have been conducted regarding the Atkinson cycle and Atkinson engine which have resulted in various thermal efficiency and output power analysis. In the present study, output power and engine thermal efficiency are maximized via employing the NSGA-II approach and thermodynamic analysis. The multi-objective evolutionary approach on the basis of the NSGA-II method is implemented throughout this work for optimizing the above-mentioned variables. To evaluate the aforementioned goal, two objective functions which comprises the power output ( W ) and cycle efficiency ( ) have been included in the optimization process simultaneously.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 71
    Publication Date: 2015-09-30
    Description: The electrical rock conductivity is a sensitive indicator for carbon dioxide (CO 2 ) injection and migration processes. For a reliable balancing of the free CO 2 in pore space with petrophysical models such as Archie's law or for the detection of migrating CO 2 , detailed knowledge of the pore water conductivity during interaction with CO 2 is essential but not available yet. Contrary to common assumptions, pore water conductivity cannot be assumed constant since CO 2 is a reactive gas that dissolves into the pore water in large amounts and provides additional charge carriers due to the dissociation of carbonic acid. We consequently carried out systematic laboratory experiments to quantify and analyse the changes in saline pore water conductivity caused by CO 2 at thermodynamic equilibrium. Electrical conductivity is measured on pore water samples for pressures up to 30 MPa and temperatures up to 80 °C. The parameter range covers the gaseous, liquid and supercritical state of the CO 2 involved. Pore water salinities from 0.006 up to 57.27 g L –1 sodium chloride were investigated as well as selective other ion species. At the same time, the CO 2 concentration in the salt solution was determined by a wet-chemical procedure. A two-regime behaviour appears: for small salinities, we observe an increase of up to more than factor 3 in the electrical pore water conductivity, which strongly depends on the solution salinity (low-salinity regime). This is an expected behaviour, since the additional ions originating from the dissociation of carbonic acid positively contribute to the solution conductivity. However, when increasing salinities are considered this effect is completely diminished. For highly saline solutions, the increased mutual impeding causes the mobility of all ions to decrease, which may result in a significant reduction of conductivity by up to 15 per cent despite the added CO 2 (high-salinity regime). We present the data set covering the pressure, temperature, salinity and ion species dependence of the CO 2 effect. Furthermore, the observations are analysed and predicted with a semi-analytical formulation for the electrical pore water conductivity taking into account the species’ interactions. For the applicability of our results in practice of exploration and monitoring, we additionally provide a purely empirical formulation to compute the impact of CO 2 on pore water conductivity at equilibrium which only requires the input of pressure, temperature and salinity information.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
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    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 72
    Publication Date: 2015-10-15
    Description: Intrinsically disordered proteins and regions (IDPs and IDRs) lack stable 3D structure under physiological conditions in-vitro , are common in eukaryotes, and facilitate interactions with RNA, DNA and proteins. Current methods for prediction of IDPs and IDRs do not provide insights into their functions, except for a handful of methods that address predictions of protein-binding regions. We report first-of-its-kind computational method DisoRDPbind for high-throughput prediction of RNA, DNA and protein binding residues located in IDRs from protein sequences. DisoRDPbind is implemented using a runtime-efficient multi-layered design that utilizes information extracted from physiochemical properties of amino acids, sequence complexity, putative secondary structure and disorder and sequence alignment. Empirical tests demonstrate that it provides accurate predictions that are competitive with other predictors of disorder-mediated protein binding regions and complementary to the methods that predict RNA- and DNA-binding residues annotated based on crystal structures. Application in Homo sapiens, Mus musculus, Caenorhabditis elegans and Drosophila melanogaster proteomes reveals that RNA- and DNA-binding proteins predicted by DisoRDPbind complement and overlap with the corresponding known binding proteins collected from several sources. Also, the number of the putative protein-binding regions predicted with DisoRDPbind correlates with the promiscuity of proteins in the corresponding protein–protein interaction networks. Webserver: http://biomine.ece.ualberta.ca/DisoRDPbind/
    Keywords: Computational Methods
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    Topics: Biology
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  • 73
    Publication Date: 2015-12-18
    Description: Although the Matuyama–Brunhes boundary (MBB) in the Chinese Loess Plateau (CLP) is very important in reliably correlating Quaternary loess with other sediments in the world, particularly with marine and polar ice cores, its exact stratigraphic position remains controversial. Previous investigations usually placed the MBB between paleosol unit S8 and loess unit L8 in various locations. To better understand the spatial differences in the MBB position, a high-resolution paleomagnetic study was conducted in a loess section of the Lantian Basin at the southern margin of the CLP. The results show that the MBB is situated in the middle of the relatively weak paleosol unit S7, consistent with a recent report on the MBB based on a 10 Be study from the Xifeng and Luochuan loess sections of the central CLP. However, the regional anomalously low magnetic susceptibility in paleosols S7 and S8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size. Then, the MBB in the Yushan section can be correlated with the bottom of paleosol S7, corresponding to the older part of interglacial marine isotope stage 19. This result temporally reconciles the striking discrepancy of the position of the MBB recorded in between loess and other typical sedimentary sequences, and further confirms that the stratigraphic position of the MBB could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the CLP. In the Yushan section, the high-frequency variations of paleomagnetic directions during a long period of ~31 ka before the MBB, however, could not be attributed to a genuine response to the true geomagnetic behaviour. Moreover, the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background. A multiproxy-based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern CLP.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 74
    Publication Date: 2015-12-18
    Description: We study rotating thermal convection in spherical shells as prototype for flow in the cores of terrestrial planets, gas planets or in stars. We base our analysis on a set of about 450 direct numerical simulations of the (magneto)hydrodynamic equations under the Boussinesq approximation. The Ekman number ranges from 10 –3 to 10 –5 . The supercriticality of the convection reaches about 1000 in some models. Four sets of simulations are considered: non-magnetic simulations and dynamo simulations with either free-slip or no-slip flow boundary conditions. The non-magnetic setup with free-slip boundaries generates the strongest zonal flows. Both non-magnetic simulations with no-slip flow boundary conditions and self-consistent dynamos with free-slip boundaries have drastically reduced zonal-flows. Suppression of shear leads to a substantial gain in heat-transfer efficiency, increasing by a factor of 3 in some cases. Such efficiency enhancement occurs as long as the convection is significantly influenced by rotation. At higher convective driving the heat-transfer efficiency tends towards that of the classical non-rotating Rayleigh–Bénard system. Analysis of the latitudinal distribution of heat flow at the outer boundary reveals that the shear is most effective at suppressing heat-transfer in the equatorial regions. Simulations with convection zones of different thickness show that the zonal flows become less energetic in thicker shells, and, therefore, their effect on heat-transfer efficiency decreases. Furthermore, we explore the influence of the magnetic field on the non-zonal flow components of the convection. For this we compare the heat-transfer efficiency of no-slip non-magnetic cases with that of the no-slip dynamo simulations. We find that at E = 10 –5 magnetic field significantly affects the convection and a maximum gain of about 30 per cent (as compared to the non-magnetic case) in heat-transfer efficiency is obtained for an Elsasser number of about 3. Our analysis motivates us to speculate that convection in the polar regions in dynamos at E = 10 –5 is probably in a ‘magnetostrophic’ regime.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 75
    Publication Date: 2015-12-19
    Description: ‘Anomalous’ magnetic fabrics in dikes that appear to indicate flow into the wall confound many workers. Here, we present extensive magnetic data on five dikes from Tenerife, Canary Islands, and use these to interpret the causes of the anomalous fabrics. Comparison of the anisotropy of magnetic susceptibility (AMS) and anhysteretic magnetization (AARM) results show that, in some cases, the anomalous fabrics are caused by single-domain grains, which produce AMS fabrics perpendicular to the grain elongation, whereas AARM fabrics are parallel. To check this, hysteresis experiments were used to characterize the domain state. These show most are mixtures of pseudo-single-domain or single-domain plus multi-domain particles, but many have wasp-waisted hysteresis loops, likely indicating mixed populations of stable single-domain and superparamagnetic grains. First-order reversal curves were used to better characterize this and show mixtures of stable single-domain and superparamagnetic grains dominate the magnetic signal. Magnetic particles at the stable single-domain/superparamagnetic threshold are unstable at timespans relevant to the analytical techniques, so they produce complicated results. This suggests that anomalous AMS fabrics in dikes cannot simply be attributed to elongated stable single-domain particles and that mixtures of the different grain types can produce hybrid fabrics, in which the fabrics are neither perpendicular or parallel to the dike plane, that are difficult to interpret without extensive magnetic analysis.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 76
    Publication Date: 2016-06-03
    Description: The sequential chain of interactions altering the binary state of a biomolecule represents the ‘information flow’ within a cellular network that determines phenotypic properties. Given the lack of computational tools to dissect context-dependent networks and gene activities, we developed NetDecoder, a network biology platform that models context-dependent information flows using pairwise phenotypic comparative analyses of protein–protein interactions. Using breast cancer, dyslipidemia and Alzheimer's disease as case studies, we demonstrate NetDecoder dissects subnetworks to identify key players significantly impacting cell behaviour specific to a given disease context. We further show genes residing in disease-specific subnetworks are enriched in disease-related signalling pathways and information flow profiles, which drive the resulting disease phenotypes. We also devise a novel scoring scheme to quantify key genes—network routers, which influence many genes, key targets, which are influenced by many genes, and high impact genes, which experience a significant change in regulation. We show the robustness of our results against parameter changes. Our network biology platform includes freely available source code ( http://www.NetDecoder.org ) for researchers to explore genome-wide context-dependent information flow profiles and key genes, given a set of genes of particular interest and transcriptome data. More importantly, NetDecoder will enable researchers to uncover context-dependent drug targets.
    Keywords: Computational Methods
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    Topics: Biology
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  • 77
    Publication Date: 2016-09-11
    Description: We derive scaling relationships for planetary dynamos based on a balance between energy production and Joule dissipation, and between the curl of the buoyancy and Coriolis forces. These scaling relationships are deduced for the particular case of dynamos driven by helical waves, but are shown to have a much broader applicability. They are consistent with the evidence of the numerical dynamos, yielding predictions consistent with published empirical scaling laws and also with the observed transition from dipolar to multipolar dynamos. A direct comparison with the observational evidence for the planets is hampered by the fact that we do not know what sets the smallest scale of the motion in the planets. Nevertheless, we use our scaling relationships to show that the traditional assumption that the Elsasser number is of order unity is inconsistent with the observation that the gas-giant dynamos are dipolar dynamos, as is the more recent suggestion that the strength of the dipole is independent of rotation rate and controlled by the buoyancy flux alone. On the other hand, we show that the observational data is consistent with the hypothesis that a dipolar dynamo saturates at the lowest permissible magnetic energy compatible with a given buoyancy flux.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
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  • 78
    Publication Date: 2016-09-14
    Description: We present a detailed palaeomagnetic study from 35 sites on Holocene lava flows of the Tongariro Volcanic Centre, central North Island, New Zealand. Prior to the study the eruption ages of these flows were constrained to within a few thousand years by recently published high-precision 40 Ar/ 39 Ar geochronological data and tephrostratigraphic controls. Correlation of flow mean palaeomagnetic directions with a recently published continuous sediment record from Lake Mavora, Fiordland, allows us to reduce the age uncertainty to 300–500 yr in some cases. Our refined ages significantly improve the chronology of Holocene effusive eruptions of the volcanoes of the Tongariro Volcanic Centre. For instance, differences in the palaeomagnetic directions recorded by lavas from the voluminous Iwikau and Rangataua members suggest that individual effusive periods lasted up to thousands of years and that these bursts have been irregularly spaced over time. While over the last few millennia the effusive eruptive activity from Mt Ruapehu has been relatively quiet, the very young age (200–500 BP) of a Red Crater sourced flow suggests that effusive activity around Mt Tongariro lasted into the past few centuries. This adds an important hazard context to the historical record, which has otherwise comprised frequent relatively small, tephra producing, explosive eruptions without the production of lava flows.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 79
    Publication Date: 2016-07-07
    Description: The inversion of magnetotelluric data into subsurface electrical conductivity poses an ill-posed problem. Smoothing constraints are widely employed to estimate a regularized solution. Here, we present an alternative inversion scheme that estimates a sparse representation of the model in a wavelet basis. The objective of the inversion is to determine the few non-zero wavelet coefficients which are required to fit the data. This approach falls into the class of sparsity constrained inversion schemes and minimizes the combination of the data misfit in a least-squares 2 sense and of a model coefficient norm in an 1 sense ( 2 - 1 minimization). The 1 coefficient norm renders the solution sparse in a suitable representation such as the multiresolution wavelet basis, but does not impose explicit structural penalties on the model as it is the case for 2 regularization. The presented numerical algorithm solves the mixed 2 - 1 norm minimization problem for the nonlinear magnetotelluric inverse problem. We demonstrate the feasibility of our algorithm on synthetic 2-D MT data as well as on a real data example. We found that sparse models can be estimated by inversion and that the spatial distribution of non-vanishing coefficients indicates regions in the model which are resolved.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
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    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 80
    Publication Date: 2015-04-19
    Description: We examined the mathematical and computational aspects of the magnetic potential, vector and gradient tensor fields of a tesseroid in a geocentric spherical coordinate system (SCS). This work is relevant for 3-D modelling that is performed with lithospheric vertical scales and global, continent or large regional horizontal scales. The curvature of the Earth is significant at these scales and hence, a SCS is more appropriate than the usual Cartesian coordinate system (CCS). The 3-D arrays of spherical prisms (SP; ‘tesseroids’) can be used to model the response of volumes with variable magnetic properties. Analytical solutions do not exist for these model elements and numerical or mixed numerical and analytical solutions must be employed. We compared various methods for calculating the response in terms of accuracy and computational efficiency. The methods were (1) the spherical coordinate magnetic dipole method (MD), (2) variants of the 3-D Gauss–Legendre quadrature integration method (3-D GLQI) with (i) different numbers of nodes in each of the three directions, and (ii) models where we subdivided each SP into a number of smaller tesseroid volume elements, (3) a procedure that we term revised Gauss–Legendre quadrature integration (3-D RGLQI) where the magnetization direction which is constant in a SCS is assumed to be constant in a CCS and equal to the direction at the geometric centre of each tesseroid, (4) the Taylor's series expansion method (TSE) and (5) the rectangular prism method (RP). In any realistic application, both the accuracy and the computational efficiency factors must be considered to determine the optimum approach to employ. In all instances, accuracy improves with increasing distance from the source. It is higher in the percentage terms for potential than the vector or tensor response. The tensor errors are the largest, but they decrease more quickly with distance from the source. In our comparisons of relative computational efficiency, we found that the magnetic potential takes less time to compute than the vector response, which in turn takes less time to compute than the tensor gradient response. The MD method takes less time to compute than either the TSE or RP methods. The efficiency of the (GLQI and) RGLQI methods depends on the polynomial order, but the response typically takes longer to compute than it does for the other methods. The optimum method is a complex function of the desired accuracy, the size of the volume elements, the element latitude and the distance between the source and the observation. For a model of global extent with typical model element size (e.g. 1 degree horizontally and 10 km radially) and observations at altitudes of 10s to 100s of km, a mixture of methods based on the horizontal separation of the source and observation separation would be the optimum approach. To demonstrate the RGLQI method described within this paper, we applied it to the computation of the response for a global magnetization model for observations at 300 and 30 km altitude.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 81
    Publication Date: 2015-04-21
    Description: limma is an R/Bioconductor software package that provides an integrated solution for analysing data from gene expression experiments. It contains rich features for handling complex experimental designs and for information borrowing to overcome the problem of small sample sizes. Over the past decade, limma has been a popular choice for gene discovery through differential expression analyses of microarray and high-throughput PCR data. The package contains particularly strong facilities for reading, normalizing and exploring such data. Recently, the capabilities of limma have been significantly expanded in two important directions. First, the package can now perform both differential expression and differential splicing analyses of RNA sequencing (RNA-seq) data. All the downstream analysis tools previously restricted to microarray data are now available for RNA-seq as well. These capabilities allow users to analyse both RNA-seq and microarray data with very similar pipelines. Second, the package is now able to go past the traditional gene-wise expression analyses in a variety of ways, analysing expression profiles in terms of co-regulated sets of genes or in terms of higher-order expression signatures. This provides enhanced possibilities for biological interpretation of gene expression differences. This article reviews the philosophy and design of the limma package, summarizing both new and historical features, with an emphasis on recent enhancements and features that have not been previously described.
    Keywords: Computational Methods
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  • 82
    Publication Date: 2015-05-20
    Description: Kamacite particles (Fe–Ni, Ni 〈 5 per cent), are very common in extra-terrestrial materials, such as meteorites. It is normally assumed that for kamacite particles to be reliable recorders of magnetic fields, they need to be magnetically uniform (single domain, SD) and thermally stable. Larger particles subdivide into non-uniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic behaviour. In this paper we determine the first micromagnetic calculation of the stable SD range domain-state phase diagram for metallic iron; previous calculations were analytical. There is a significant increase in the critical size for the SD/MD threshold size, for example, for cube-shaped iron particles, the critical SD/MD threshold has now been estimated to be 25 nm, compared to 17 nm for previous estimates. The larger critical SD/MD threshold size for iron, agrees better with previously published nanometric observations of domain state for FeNi particles, then early analytical models.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 83
    Publication Date: 2015-05-22
    Description: This paper presents a distributed magnetotelluric inversion scheme based on adaptive finite-element method (FEM). The key novel aspect of the introduced algorithm is the use of automatic mesh refinement techniques for both forward and inverse modelling. These techniques alleviate tedious and subjective procedure of choosing a suitable model parametrization. To avoid overparametrization, meshes for forward and inverse problems were decoupled. For calculation of accurate electromagnetic (EM) responses, automatic mesh refinement algorithm based on a goal-oriented error estimator has been adopted. For further efficiency gain, EM fields for each frequency were calculated using independent meshes in order to account for substantially different spatial behaviour of the fields over a wide range of frequencies. An automatic approach for efficient initial mesh design in inverse problems based on linearized model resolution matrix was developed. To make this algorithm suitable for large-scale problems, it was proposed to use a low-rank approximation of the linearized model resolution matrix. In order to fill a gap between initial and true model complexities and resolve emerging 3-D structures better, an algorithm for adaptive inverse mesh refinement was derived. Within this algorithm, spatial variations of the imaged parameter are calculated and mesh is refined in the neighborhoods of points with the largest variations. A series of numerical tests were performed to demonstrate the utility of the presented algorithms. Adaptive mesh refinement based on the model resolution estimates provides an efficient tool to derive initial meshes which account for arbitrary survey layouts, data types, frequency content and measurement uncertainties. Furthermore, the algorithm is capable to deliver meshes suitable to resolve features on multiple scales while keeping number of unknowns low. However, such meshes exhibit dependency on an initial model guess. Additionally, it is demonstrated that the adaptive mesh refinement can be particularly efficient in resolving complex shapes. The implemented inversion scheme was able to resolve a hemisphere object with sufficient resolution starting from a coarse discretization and refining mesh adaptively in a fully automatic process. The code is able to harness the computational power of modern distributed platforms and is shown to work with models consisting of millions of degrees of freedom. Significant computational savings were achieved by using locally refined decoupled meshes.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 84
    Publication Date: 2015-06-19
    Description: A spatially averaged mean-field model for fully or partially ordered members of the ilmenite–hematite solid solution series is rigorously derived from the Heisenberg Hamiltonian by first assuming no temporal correlation of atomic spins, and then by spatially averaging over spins at equivalent atomic positions. The model is based on the geometry of exchange interactions between nearest and next-nearest neighbours and predicts magnetization curves in homogenous solid solutions with variable degree of order. While the general framework presented can also be applied to atomic scale models, and to other solid solution series, here the symmetries of the ilmenite–hematite lattice are exploited to show that four different sublattice magnetizations and six independent combinations of exchange constants determine the temperature variation of the magnetization curves. Comparing measured Curie temperatures T C and M s ( T ) curves to model predictions results in accurate constraints for these combinations. It is also possible to calculate predictions for high-field magnetization slopes HF , which not only improve accurate experimental determination of the Curie temperature but also provide a new magnetic method to estimate the order parameter for ilmenite–hematite solid solution samples.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 85
    Publication Date: 2015-02-12
    Description: Tibetan Plateau uplift and global cooling have generally been thought to have caused the drying of the Asian inland, but how and when these factors drove the aridification is unknown. The Xining Basin at the NE Tibetan Plateau received continuous Eocene–Miocene fine-grained sediments, providing an excellent opportunity to address this question. Here we present detailed rock magnetic and diffuse reflectance spectroscopy (DRS) analyses for a well-dated Cenozoic sedimentary record from the Xiejia section in the basin. Magnetic susceptibility ( ), saturation magnetization (Ms) and saturation isothermal remanent magnetization (SIRM) in this section show a long-term decreasing trend from ~52 to ~25 Ma, well coinciding with global cooling and drying in the region, and an increasing trend since ~25 Ma, which is in contrast to the further progressing aridification of the basin. Thermomagnetic results and DRS-determined hematite contents suggest that the relative content of magnetite and hematite is the main control on the , Ms and SIRM values. We argue that the long-term Eocene–Oligocene global cooling increased the drying of the Asian inland, lowering the lake level and exposing a larger area to low temperature oxidation for longer times, thus producing more hematite and leading to the decreasing trend of magnetic concentration parameters from ~52 to ~25 Ma. An intensive uplift of the NE Tibetan Plateau since ~25 Ma, associated with a change in the sedimentary source, might be responsible for the increase of , Ms and SIRM after 25 Ma.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
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  • 86
    Publication Date: 2015-02-18
    Description: Protein sequences predicted from metagenomic datasets are annotated by identifying their homologs via sequence comparisons with reference or curated proteins. However, a majority of metagenomic protein sequences are partial-length, arising as a result of identifying genes on sequencing reads or on assembled nucleotide contigs, which themselves are often very fragmented. The fragmented nature of metagenomic protein predictions adversely impacts homology detection and, therefore, the quality of the overall annotation of the dataset. Here we present a novel algorithm called GRASP that accurately identifies the homologs of a given reference protein sequence from a database consisting of partial-length metagenomic proteins. Our homology detection strategy is guided by the reference sequence, and involves the simultaneous search and assembly of overlapping database sequences. GRASP was compared to three commonly used protein sequence search programs (BLASTP, PSI-BLAST and FASTM). Our evaluations using several simulated and real datasets show that GRASP has a significantly higher sensitivity than these programs while maintaining a very high specificity. GRASP can be a very useful program for detecting and quantifying taxonomic and protein family abundances in metagenomic datasets. GRASP is implemented in GNU C++, and is freely available at http://sourceforge.net/projects/grasp-release .
    Keywords: Computational Methods
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  • 87
    Publication Date: 2015-02-18
    Description: Genetic screens of an unprecedented scale have recently been made possible by the availability of high-complexity libraries of synthetic oligonucleotides designed to mediate either gene knockdown or gene knockout, coupled with next-generation sequencing. However, several sources of random noise and statistical biases complicate the interpretation of the resulting high-throughput data. We developed HiTSelect, a comprehensive analysis pipeline for rigorously selecting screen hits and identifying functionally relevant genes and pathways by addressing off-target effects, controlling for variance in both gene silencing efficiency and sequencing depth of coverage and integrating relevant metadata. We document the superior performance of HiTSelect using data from both genome-wide RNAi and CRISPR/Cas9 screens. HiTSelect is implemented as an open-source package, with a user-friendly interface for data visualization and pathway exploration. Binary executables are available at http://sourceforge.net/projects/hitselect/ , and the source code is available at https://github.com/diazlab/HiTSelect .
    Keywords: Computational Methods
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  • 88
    Publication Date: 2015-01-24
    Description: Integrative analyses of epigenetic data promise a deeper understanding of the epigenome. Epidaurus is a bioinformatics tool used to effectively reveal inter-dataset relevance and differences through data aggregation, integration and visualization. In this study, we demonstrated the utility of Epidaurus in validating hypotheses and generating novel biological insights. In particular, we described the use of Epidaurus to (i) integrate epigenetic data from prostate cancer cell lines to validate the activation function of EZH2 in castration-resistant prostate cancer and to (ii) study the mechanism of androgen receptor ( AR ) binding deregulation induced by the knockdown of FOXA1 . We found that EZH2 's noncanonical activation function was reaffirmed by its association with active histone markers and the lack of association with repressive markers. More importantly, we revealed that the binding of AR was selectively reprogramed to promoter regions, leading to the up-regulation of hundreds of cancer-associated genes including EGFR . The prebuilt epigenetic dataset from commonly used cell lines (LNCaP, VCaP, LNCaP-Abl, MCF7, GM12878, K562, HeLa-S3, A549, HePG2) makes Epidaurus a useful online resource for epigenetic research. As standalone software, Epidaurus is specifically designed to process user customized datasets with both efficiency and convenience.
    Keywords: Computational Methods
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  • 89
    Publication Date: 2015-01-29
    Description: The Mt Amram igneous complex (AIC) represents northern tip of the Neoproterozoic Arabian Nubian Shield (ANS). For the first time the AIC deep structure was studied using the gravity, aero and ground magnetic, magnetic susceptibility and density measurements and geological data. Analysing all available data at the Amram area we concluded what only monzonite body can be reason for gravity high and coinciding reduced to pole (RTP) maximum. Geological knowledge allowed suggesting its intrusive character and compact body form. Cluster of inverse solutions (Werner deconvolution) localized this body as initial model for forward modelling. Further iterations (2 3/4 -D forward modelling) clarified the monzonite geometry and properties; the modelling allowed also to investigate the non-uniqueness and estimate also the confident intervals for final solution. The research consists three interconnected stages. At the detailed scale, ground magnetic data suggested three magmatic blocks of few hundred meters shifted dextral about 100 m along the Zefunut fault. Estimated accuracy for geometry of the magnetic bodies is a few tens metres. At the middle scale, quantitative gravity and magnetic interpretations provide model of the monzonite body, which is an order of magnitude more than the volume of the felsic rhyolites and granite rocks. Boundary of the whole monzonite body was estimated with accuracy as a hundred meters. As a result we suggest that the parent magma for the AIC is the monzonite, similar to the model suggested for the Timna Igneous Complex 12 km north of the AIC. The model developed can be applied to evaluate the subsurface volumes of the mafic magmatic rocks in adjacent locations. At the regional scale for exposed the Sinai and Arab Saudi Precambrian crystalline shield our approach allows to understand the apparent contradiction between geological predominantly granite composition (low magnetic rocks) and magnetic data. The aeromagnetic data show number strong magnetic anomalies suggesting the presence large volume of high magnetic (mainly basic) rocks at the depth. This problem is proposed for future research.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 90
    Publication Date: 2015-01-29
    Description: 3-D electromagnetic (EM) studies of the Earth have advanced significantly over the past decade. Despite a certain success of the 3-D EM inversions of real data sets, the quantitative assessment of the recovered models is still a challenging problem. It is known that one can gain valuable information about model uncertainties from the analysis of Hessian matrix. However, even with modern computational capabilities the calculation of the Hessian matrix based on numerical differentiation is extremely time consuming. Much more efficient way to compute the Hessian matrix is provided by an ‘adjoint sources’ methodology. The computation of Hessian matrix (and Hessian-vector products) using adjoint formulation is now well-established approach, especially in seismic inverse modelling. As for EM inverse modelling we did not find in the literature a description of the approach, which would allow EM researchers to apply this methodology in a straightforward manner to their scenario of interest. In the paper, we present formalism for the efficient calculation of the Hessian matrix using adjoint sources approach. We also show how this technique can be implemented to calculate multiple Hessian-vector products very efficiently. The formalism is general in the sense that it allows to work with responses that arise in EM problem set-ups either with natural- or controlled-source excitations. The formalism allows for various types of parametrization of the 3-D conductivity distribution. Using this methodology one can readily obtain appropriate formulae for the specific sounding methods. To illustrate the concept we provide such formulae for two EM techniques: magnetotellurics and controlled-source sounding with vertical magnetic dipole as a source.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 91
    Publication Date: 2015-02-12
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 92
    Publication Date: 2015-02-18
    Description: RNA-protein complexes are essential in mediating important fundamental cellular processes, such as transport and localization. In particular, ncRNA-protein interactions play an important role in post-transcriptional gene regulation like mRNA localization, mRNA stabilization, poly-adenylation, splicing and translation. The experimental methods to solve RNA-protein interaction prediction problem remain expensive and time-consuming. Here, we present the RPI-Pred (RNA-protein interaction predictor), a new support-vector machine-based method, to predict protein-RNA interaction pairs, based on both the sequences and structures. The results show that RPI-Pred can correctly predict RNA-protein interaction pairs with ~94% prediction accuracy when using sequence and experimentally determined protein and RNA structures, and with ~83% when using sequences and predicted protein and RNA structures. Further, our proposed method RPI-Pred was superior to other existing ones by predicting more experimentally validated ncRNA-protein interaction pairs from different organisms. Motivated by the improved performance of RPI-Pred, we further applied our method for reliable construction of ncRNA-protein interaction networks. The RPI-Pred is publicly available at: http://ctsb.is.wfubmc.edu/projects/rpi-pred .
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 93
    Publication Date: 2015-02-18
    Description: Identifying conserved and divergent response patterns in gene networks is becoming increasingly important. A common approach is integrating expression information with gene association networks in order to find groups of connected genes that are activated or repressed. In many cases, researchers are also interested in comparisons across species (or conditions). Finding an active sub-network is a hard problem and applying it across species requires further considerations (e.g. orthology information, expression data and networks from different sources). To address these challenges we devised ModuleBlast, which uses both expression and network topology to search for highly relevant sub-networks. We have applied ModuleBlast to expression and interaction data from mouse, macaque and human to study immune response and aging. The immune response analysis identified several relevant modules, consistent with recent findings on apoptosis and NFB activation following infection. Temporal analysis of these data revealed cascades of modules that are dynamically activated within and across species. We have experimentally validated some of the novel hypotheses resulting from the analysis of the ModuleBlast results leading to new insights into the mechanisms used by a key mammalian aging protein.
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 94
    Publication Date: 2015-02-18
    Description: Here we used discriminative training methods to uncover the chromatin, transcription factor (TF) binding and sequence features of enhancers underlying gene expression in individual cardiac cells. We used machine learning with TF motifs and ChIP data for a core set of cardiogenic TFs and histone modifications to classify Drosophila cell-type-specific cardiac enhancer activity. We show that the classifier models can be used to predict cardiac cell subtype cis -regulatory activities. Associating the predicted enhancers with an expression atlas of cardiac genes further uncovered clusters of genes with transcription and function limited to individual cardiac cell subtypes. Further, the cell-specific enhancer models revealed chromatin, TF binding and sequence features that distinguish enhancer activities in distinct subsets of heart cells. Collectively, our results show that computational modeling combined with empirical testing provides a powerful platform to uncover the enhancers, TF motifs and gene expression profiles which characterize individual cardiac cell fates.
    Keywords: Computational Methods
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 95
    Publication Date: 2015-01-24
    Description: Geomagnetic jerks are sudden changes of trend in the geomagnetic secular variation. The Earth's mantle behaves as a filter for the jerks, causing a delayed and a smoothed signal at the Earth's surface. Backus' mantle filter theory relies on approximating the impulse response function (IRF) of the mantle by a Gaussian. The advantage of this theory is the linear relation between jerks’ delay times and the mantle electrical conductivity, as expressed by kernels. However, the limitations of this theory arise when negative delay and/or smoothing times occur. The applicability of the mantle filter theory is examined by analysing the validity of the Gaussian as an approximation for the composite IRF (CIRF) at a given location. We show that the electrical conductivity of the lower mantle is mostly responsible for the jerk delay time. Alternating sign CIRFs might cause negative delay and/or smoothing times which prevents the use of the mantle filter theory. Adequate/inadequate Gaussian approximations to the CIRFs give small/large differences in the convolved jerk occurrence times. Most observatories yield positive time constants, but in most cases the difference in the jerk occurrence times exceeds 0.5 yr.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 96
    Publication Date: 2015-07-09
    Description: A new method of estimating fluid flows near the core–mantle boundary is presented. Both the geomagnetic diffusion and dynamics in a boundary layer are taken into account under the no-slip condition at the core–mantle boundary. Below the boundary layer, the tangentially geostrophic constraint is imposed on the flow to be estimated. The radial component of the geomagnetic field just within the core is calculated from the radial component and its partial derivatives with respect to the radius, first, derived from continuity of the solenoidal field across the finite jump in electrical conductivity and, second, the geomagnetic diffusion. Below the boundary layer, fluid motions thus derived show some features common to those estimated on the basis of the frozen-flux approximation, and their accompanying vortices at mid and high latitudes are well correlated with upwellings or downwellings inside the boundary layer. The positional relation of upwellings and downwellings in equatorial regions inside and below the boundary layer suggests existence of columnar convective cells there. Intense magnetic flux spots seen in equatorial regions are likely to be produced not by downwellings at tops of cyclonic columns but by flux expulsion due to upwellings between adjacent columnar flows. The present new method leads to a new insight on core surface flows that have not been noted so far.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 97
    Publication Date: 2015-07-12
    Description: In most numerical simulations of the Earth's core the dynamo resides outside the tangent cylinder and may be crudely classified as being of the α 2 type. In this region the flow comprises a sea of thin columnar vortices aligned with the rotation axis, taking the form of alternating cyclones and anticyclones. The dynamo is thought to be driven by these columnar vortices within which the flow is observed to be highly helical, helicity being a crucial ingredient of planetary dynamos. As noted in Davidson, one of the mysteries of this dynamo cartoon is the origin of the helicity, which is observed to be positive in the south and negative in the north. While Ekman pumping at the mantle can induce helicity in some of the overly viscous numerical simulations, it is extremely unlikely to be a significant source within planets. In this paper we return to the suggestion of Davidson that the helicity observed in the less viscous simulations owes its existence to helical wave packets, launched in and around the equatorial plane where the buoyancy flux is observed to be strong. Here we show that such wave packets act as a potent source of planetary helicity, constituting a simple, robust mechanism that yields the correct sign for h north and south of the equator. Since such a mechanism does not rely on the presence of a mantle, it can operate within both the Earth and the gas giants. Moreover, our numerical simulations show that helical wave packets dispersing from the equator produce a random sea of thin, columnar cyclone/anticyclone pairs, very like those observed in the more strongly forced dynamo simulations. We examine the local dynamics of helical wave packets dispersing from the equatorial regions, as well as the overall nature of an α 2 -dynamo driven by such wave packets. Our local analysis predicts the mean emf induced by helical waves, an analysis that rests on a number of simple approximations which are consistent with our numerical experiments, while our global analysis yields exact integral relationships between the mean emf induced by the wave packets and the large-scale dipole and azimuthal field. Combining these local and integral equations yields a kinematic model for an α 2 -dynamo driven by helical waves. Order-of-magnitude estimates based on these equations suggest that such a dynamo is indeed feasible.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 98
    Publication Date: 2015-07-12
    Description: The Lower Danube Basin is one of the most important loess regions from Europe, which have provided excellent archives for long-term high-resolution palaeoclimate studies. The aim of this paper is to derive new information on the Middle–Late Pleistocene palaeoenvironment from a high resolution multiproxy assessment of the iron mineralogical composition at the Costinesti loess-palaeosol sequence located on the western Black Sea shore. It is the easternmost loess section in the Romanian loess region studied and its distinct pattern of the proxy records can be used to correlate the lower Danube loess to other key sites of the Moldavia and Ukraine loess regions. To investigate the climatic control on soft and hard ferromagnetic minerals we used several types of rock magnetic properties: magnetic susceptibility and its frequency dependence, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis properties and FORC distributions, an unmixing model for isothermal remanent magnetization curves and high field (up to 8 T) isothermal remanence measurements. Our results show that the palaeosol horizons, formed during interglacials and climatically more favored periods of the Pleistocene, experienced pedogenic alteration, resulting in high amounts of superparamagnetic, single domain and pseudosingle domain magnetite/maghemite grains and hematite. The loess layers, formed during glacial periods, are mainly dominated by multidomain and/or pseudosingle domain oxidized magnetite and some hematite, all probably of aeolian origin. Goethite contribution is probably minor and constant both in loess and palaeosol horizons. We review the correlation of the loess sections from the lower Danube basin concluding that the new results can be interpreted as a support for the transition of a Mediterranean type climate to a steppe type climate in the last two interglacial periods in the western Black Sea. Because the pattern of magnetic susceptibility data from the lower Danube basin is changing relative fast with distance from the Black Sea shore, it probably reflects the local influence of the Black Sea on continental scale climatic oscillations during the last 600 ka. The values of background magnetic susceptibility of the Romanian loess-palaeosol sections indicate that the main source area of the dust changed during this climatic transition. Our analysis also shows that the age of the loess-palaeosol sections from the Eastern European low lands (Moldavia and Ukraine) must be revised to be in agreement with the chronostratigraphy of the sections from the Lower Danube Basin loess area.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 99
    Publication Date: 2015-07-04
    Description: Statistical models of geomagnetic secular variations in terms of a Giant Gaussian Process (GGP) are compared with palaeontensity databases (Brunhes epoch, effusive rocks). We tested two GGP models TK and QC (suggested by Tauxe-Kent and Quidelleur-Courtillot) against 392 volcanic palaeointensity data, and found both models to be incompatible with the data. Even though at present there is no accepted GGP model of the Brunhes chron, we found interesting to clarify the details of this negative test. While such an incompatibility is clear enough for the TK model, because of its too small dipole coefficient, the incompatibility of the QC model was due the 12 per cent of the data with very small intensities; remaining 88 per cent of data is fully compatible with QC model QC. The troublesome, low-palaeointensity records belong to different sites and ages so their excess presence is not an effect of particular location or time. We found no evidence that the marked discrepancy between the empirical data and theoretical calculations on the QC model can be explained by the possibility that the low-intensity values belong to known excursions of the geomagnetic field. As an alternative, we conjecture that selected low-intensity values can possibly stem from acquisition of chemical remanent magnetization instead of the thermoremanence.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 100
    Publication Date: 2015-07-17
    Description: A new method of estimating fluid flows near the core–mantle boundary is presented. Both the geomagnetic diffusion and dynamics in a boundary layer are taken into account under the no-slip condition at the core–mantle boundary. Below the boundary layer, the tangentially geostrophic constraint is imposed on the flow to be estimated. The radial component of the geomagnetic field just within the core is calculated from the radial component and its partial derivatives with respect to the radius, first, derived from continuity of the solenoidal field across the finite jump in electrical conductivity and, second, the geomagnetic diffusion. Below the boundary layer, fluid motions thus derived show some features common to those estimated on the basis of the frozen-flux approximation, and their accompanying vortices at mid and high latitudes are well correlated with upwellings or downwellings inside the boundary layer. The positional relation of upwellings and downwellings in equatorial regions inside and below the boundary layer suggests existence of columnar convective cells there. Intense magnetic flux spots seen in equatorial regions are likely to be produced not by downwellings at tops of cyclonic columns but by flux expulsion due to upwellings between adjacent columnar flows. The present new method leads to a new insight on core surface flows that have not been noted so far.
    Keywords: Geomagnetism, Rock Magnetism and Palaeomagnetism
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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